All you have to do is edit the bot code and basically make your own version of the bots. That or replace one of the default 9 character models with your custom models. You are still limited to the 9 characters, and even if they look different they are still the default characters.
The bots were coded specially for ESF. They have no code that handles stuff like ECX characters and attack since they were not made for it. They will allso never transform past SSJ cause thats not possible in ESF 1.2.3, so unless you code your own bot you can not add ECX characters as bots. You can change their looks and have Goku look like broll. But his attacks will still be those of Goku.
Thanks Greg, that cleared up a few things for me.
Would you be able to give me a walkthrough on how to replace the default models with the ECX ones? Doesn't matter if they don't go past SSJ they look good
Here i'll list the replacements for them
9 Regular bots into...
Goku --> Goku regular from ECX
Krillin --> ECX Krillen
Gohan --> Adult ECX Gohan *Blue Gi*
Vegeta ---> Buu Saga Vegeta
Buu ---> ECX Buu *Idk if the models are different*
Cell ---> ECX Cell *Again same as above*
Trunks ---> ECX Sword Trunks
Piccolo ---> ECX Piccolo
Frieza ---> ECX Frieza
Again if this is too much it's fine I just want to know how to replace the models and where the 9 originals are