Hello and thank you a lot for your detailed explanation !
I have managed to do the replacement, and it doesn't seem to work, the command squad will still get the speech from the last member to join it.
BUT
i think i know whats wrong. As i said earlier, im using the TitaniumWars mod and i make my modifications directly on a copy of the mod module and sga files.
So maybe the original creator made some modifications for the command squad, and maybe on the units that join it as well.
I should copy to back up, and then try to modify every unit (in this case, the commissar will be my target) speech for the captain one and see if it works