I would not modify any GM controller, it's just not built to handle anything over 20 amps constant!
I'm speaking from experience and toasted 4 of them!
I still can NOT believe they don't have any higher power controllers something like 48-72 volts up to 60 amp controller. A real continuous power not peak! And the option to change the regen, voltage, current etc from software, or even better from a display unit on the handle bars would be so cool!
The option to adjust the controller on the fly would be fantastic, and if the display could be your speedo, odometer, current, watts readings, consumption for battery monitoring. Or the option to monitor the cells for lipo users would be so cool too!
GM have no idea how well they would sell even at 200 Euros people would buy them with features like that!