2012 68RFE Tuning over someone elses tune ?

[staytuned]

Have a customer with a 2012 68RFE and tuned by another shop. Custom engine mods, turbo, deletes etc. We built a custom trans with billet drum, HD packs, big sprag etc. When built we installed the BD plate kit with box that connects to map sensor and mods the pressure.Customer complained of too harsh of shift. We removed box and had tuner shop set pressure to 225. I verified and it has good pressure rise but only above a medium throttle setting. It shifts a bit smoother but now squeals sometimes on 2-3 shift light throttle.

I need to tune this myself but it has a locked tune with efi live. Can I tune the trans side only and overwrite over their locked tune on trans side only ? and leave the engine side alone ? I know this can be done on earlier 08 version with HPT but this has the combined TCM ECM.

[GMPX]

Those ECM's cannot be read out anyway (even stock) so you would not be able to save what is in there.
Your only option is to beg that the tuner gives you the tune unlocked if you want to play with it yourself.