Hi, Okawa.
I have one idea of X02T.
We have already had the key to Encryption of two models that is TG01 and T01A(great thanks for cotulla).
I checked the key to two models.
There is a key that is actually used as follows.
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TG01 DES Key(Mode ECB)
[(4 or 5)(4 or 5)(4 or 5)(6 or 7)(0 or 1)(0 or 1)(4 or 5)(2 or 3)]
Key = 54470152(Cotulla), 45561043 and 44460042 etc.
T01A DES Key(Mode ECB)
[(4 or 5)(4 or 5)(4 or 5)(6 or 7)(0 or 1)(0 or 1)(4 or 5)(4 or 5)]
Key = 54460044(Cotulla) and 44460044(2channel) etc.
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I suppose the following from these things.
[TG01(Key is 44460042)→ T01A(Key is 44460044)→ X02T?(Key is 44460046 or 8)]
So, I guess X02T DES Key is 44460046 or 44460048, perhaps this Key is tss.
But, we do not have official Softibank ROM.
Therefore, you can not return Softibank ROM from your ROM if you Flashed.
(The method of how to make available ROM from RAW has not found yet. Maybe,)
However, if you try this key to X02T, I yell for you.(not beer

)
If this my article is useful for you, I am glad.
Thanks.