So I answer my own question :
So I used this :
Barsik-Barbosik/Zoom-Firmware-Editor
And I successfully "inject" GK & Eden amp model from MS60B into my MS70CDR
View attachment 3842645
Basically what it does is extracting models from a source firmware (MS60B in my case), save them on files and inject those files containing models into destination firmware (MS70CDR in my case). The modified firmware (with new models on it) is then flashed into the unit using normal firmware update procedure from Zoom.
For some reason I only managed to inject those 2 amps model, others failed (tested with GK, Eden, Hartke & SVT). It seems that the firmware is very sensitive or there's some underlying differences on software architecture between MS60 & MS70, as even the injection order matters. For example : inject GK then Eden works, but the inverse failed. I'll do more test tomorrow, including injecting models from MS70, G1on or MS50G into B1on.
Regardless of the problem, the guy who wrote the apps deserves a big appreciation