In Srila Jiva Goswami´s “Bhakti Sandarbha”, Anuccheda 112, we find more shastric evidence for the siddha deha being NOT inherent in the svarupa of the jiva.

Here is the Anuccheda in full (taken from the edition of Srila Satyanarayana das Babaji):

Bhakti continues even at the stage of liberation

Scriptures describe that bhakti is performed even after the heart is made free from the desire for kama by love of God, as the Lord said: 

“Just as gold gives up its impurities and becomes pure when melted in fire, the soul [atma] casts aside the seeds of karma through devotion to Me and thereafter becomes established in service to Me.”
(Srimad Bhagavatam, 11.14.25)

The meaning of this statement is that the atma, which here refers to the jiva soul, casts aside the seeds of karma by developing love for the Lord. Thereafter, he or she becomes situated in his or her pure form and identity and renders service to the Lord.

This is referred to in a statement of Sarvajna Muni cited by Sridhar Svami in his commentary on Srimad Bhagavatam:

“Even liberated souls accept a body out of their free will [playfully] and thus worship the Lord.”
(tika by Sridhar Svami to Srimad Bhagavatam, 10.87.21) 

Here are several points worthy of our attention.

First of all, we receive the information that even AFTER liberation, the sadhaka performs bhakti in a suitable body (siddha deha).

Here, liberation refers to the stage called “jivan mukti”, which the Gaudiya Vaishnavas define as being free from any material desires while still having a material body, but shortly before attaining a suitable spiritual body.

Srila Jiva Goswami explains this kind of liberation here as “having cast aside the seeds of karma by developing love for Krishna.”

So, after liberation and after our sadhaka deha perishes, the sadhaka attains a spiritual body suitable for the desired relationship with the Lord and the service performed in that siddha deha.

Srila Jiva Goswami says the sadhaka BECOMES SITUATED in the pure form and identity (siddha deha). It is a PROCESS of BECOMING, not a process of UNCOVERING.
A TRANSFORMATION, not an AWAKENING.
The jiva soul, the atma, is situated in maya-sakti (material body, bound to perish) since beginningless time and can become situated in svarupa-sakti (spiritual body, which is an eternal body) via the process of bhakti.

Now perfection in bhakti, attaining svarupa siddhi, means becoming situated in our spiritual identity.

When we are situated in our material body, we THINK that we ARE this material body.
When we become situated in our spiritual body, we ARE this spiritual body.
We don´t experience a difference like now between body and soul.
We completely ARE that wonderful spiritual body. It is our eternal identity.

It is not that this wonderful siddha deha is already present in our jiva soul [atma].

tvaṁ bhakti-yoga-paribhāvita-hṛt-saroja
āsse śrutekṣita-patho nanu nātha puṁsām
yad-yad-dhiyā ta urugāya vibhāvayanti
tat-tad-vapuḥ praṇayase sad-anugrahāya
(Srimad Bhagavatam 3.9.11)

“O Lord! You, who are approached by being heard about, seen and directly served, enter and remain in the lotus of your devotee’s hearts infused with bhakti-yoga. Much praised Lord! By your mercy, you bestow to them spiritual bodies appropriate to the mood they cultivate during sādhana.”

Srila Viśvanātha Cakravartī Ṭhākura explains – te sādhaka-bhaktāḥ sva sva bhāvānurūpaṁ yad yad dhiyā bhāvayanti tat tad eva vapus teṣāṁ siddha dehaṁ praṇayase prakarṣeṇa tān prāpayasi aho te sva bhakta pāravaśyam iti bhāvaḥ –

“Or your devotees doing sādhana concentrate on their spiritual form per their mood of love using their minds, and you have them attain (praṇayase) their spiritual bodies. You become dependent on your devotee.”

The siddha deha is bestowed by the Lord. It is attained by the sadhaka per their mood of love, not per their already existing seed of a certain siddha deha.

Sridhar Svami writes in this above-mentioned commentary on Srimad Bhagavatam, 10.87.21:

“Even liberated souls accept a body out of their free will and thus worship the Lord.”  

A liberated soul ACCEPTS a spiritual body OUT OF FREE WILL…not because it is already present as a seed form in his/her heart.

If the spiritual body would be eternally there in the heart as a seed, how can the jiva soul [atma] then attain final and thus eternal mukti [sayujiya-mukti] and choose NOT to attain a spiritual body?

It is certainly not the case that the liberated soul, desiring the eternal merging with Bhraman, recognizes the seed of a siddha deha and then decides to send it back to the Lord like a package to Amazon.

The Vedanta Sutra discusses the state of the mukta (liberated soul) in liberation, once they have given up their material body.

Baladeva Vidyabhusana Prabhu’s own commentaries in his Govinda Bhasya confirm that the liberated sadhaka can either accept a spiritual body (or even several) or he can have no body (sayujiya-mukti).

Vedanta Sutra 4.4.12

ataḥ satya-saṅkalpatvād eva hetor ubhaya-vidhaṁ muktaṁ bhagavān bādarāyaṇo manyate ubhaya-vidha-vākya-darśanāt | tam avigrahaṁ sa-vigrahaṁ ca svīkarotīty arthaḥ | dvādaśāhavat | tathā dvādaśāhasya yajamānecchayāneka-yajamānakatve satratvam eka-yajamānakatve’hīnatvaṁ ca na virudhyate | tathā svecchayāvigrahatvaṁ sa-vigrahatvaṁ ca muktasyety arthaḥ |idam atra tattvam—muktāḥ khalu brahma-vidyayā saṁchinna-pidhānāḥ satya-saṅkalpāś ca bhavanti | teṣu ye vigrahādi-lipsavas te saṅkalpād eva tadvantaḥ syuḥ | sa ekadhety ādi śruteḥ | ye tu na tādṛśās te kila na tadvantaḥ | aśarīraṁ vāvety ādi śruteḥ | ye brāhmaṇa-vapuṣā nityaṁ brahmānuvṛttim icchanti, teṣāṁ tu tac-cic-chakti-mayaṁ tad āvirbhavatīti kil nityaṁ tadvantas tad anuvartanta iti mantavyam –

“Now, since (the liberated self) is satya-sankalpa (one whose desires are instantly fulfilled), Badarayana Rishi (Vyasadeva) thinks that the liberated self can be “of both kinds”, since we find Sruti statements to both effects. 

The meaning is that he accepts that it can have a body or be without one. Just like the Dvadashaha sacrifice. According to the desire of the sponsor (yajamana) of the Dvadashaha, the sacrifice can be a Satra when it has many sponsors or an Ahina when there is only one sponsor. There is no contradiction here. The meaning is that in the same way, the liberated soul by its own will be without a body or accept a body. This is the truth — by Brahma-vidya, the liberated ones have cut away all coverings and become satya-sankalpas.

Among them, those who desire a body become like that just by that desire, as the “he becomes one, two, eleven, etc…”- Sruti statement says (Chandogya 7.26.2). 

But those who are not like that will not become such (spiritually embodied), just as the “it is certainly bodiless” – Sruti statement says (Chandogya 8.12.1).

So, if the siddha deha would already be in every jiva soul [atma], there would never ever be the question of accepting such a suitable body or not accepting a spiritual body [sayujiya-mukti].

If the siddha deha would already be present as a seed in all jiva souls [atmas], all these comments would be rendered meaningless and the liberated jiva soul would be FORCED to BE the siddha deha that is already as a seed in the heart.

te sādhaka-bhaktāḥ sva sva bhāvānurūpaṁ yad yad dhiyā bhāvayanti tat tad eva vapus teṣāṁ siddha dehaṁ praṇayase prakarṣeṇa tān prāpayasi aho te sva bhakta pāravaśyam iti bhāvaḥ –

“Or your devotees doing sādhana concentrate on their spiritual form per their mood of love using their minds, and you have them attain (praṇayase) their spiritual bodies. You become dependent on your devotee.”
(Srila Viśvanātha Cakravartī Ṭhākura)

The siddha deha is BESTOWED by the Lord and ATTAINED by the loving sadhakas.

It is a matter of MERCY, not a matter of anything being “pre-arranged” or “pre-fixed”.

There is no eternally fixed blueprint in the heart of the jiva soul [atma] determining which suitable siddha deha the jiva soul will attain.

Srila Jiva writes in his commentary to Bhakti Rasamrita Sindhu, verse 2.5.13:

This verse shows how devotee association acts as the seed of rati. Through association with various types of devotees, various types of sadhana which are like watering the seed will be performed.

bhavāpavargo bhramato yadā bhavej
janasya tarhy acyuta sat-samāgamaḥ
sat-saṅgamo yarhi tadaiva sad-gatau
parāvareśe tvayi jāyate matiḥ
(SB 10.51.53)

“When the material life of a wandering soul has ceased, O Acyuta, he may attain the association of Your devotees. And when he associates with them, then devotion unto You will start, You Who are the goal of the devotees and the Lord of all causes and their effects”.

The ultimate cause is always MERCY, KRIPA.
Everything is BESTOWED…the bhakti-lata-bija, bhava, prema and a suitable siddha deha:

anarpita-carim cirat karunayavatirnah kalau
samarpayitum unnatojjvala-rasam sva-bhakti-sriyam
harih purata-sundara-dyuti-kadamba-sandipitah
sada hrdaya-kandare sphuratu vah saci-nandanah 

“May the Supreme Lord who is known as the son of Srimati Saci-devi be transcendentally situated in the innermost chambers of your heart. Resplendent with the radiance of molten gold, He has appeared in the Age of Kali by His causeless mercy to BESTOW what no incarnation has ever offered before: the most sublime and radiant mellow of devotional service, the mellow of conjugal love.”
(Caitanya-Caritamrta Adi-lila 1.4)