Thanks for the updates. In the meantime, can I use two instances of the Fission plugin to process the same audio (Transients on the one hand and the other Tonal) and reassembling it manually? Would I have the same recomposition that should make Fission inside without creating artifacts?

Yes, that would work, providing the STRUCTURAL SPLIT sections have the same settings. With no effects on, the Transient and Tonal streams are complementary.