Modifying Creator Pro firmware

For years I have wanted to make minor modifications to the firmware in my Creator Pro. In particular, to change when the heaters turn off – but if it were manageable, I might add a couple of extra features. Has anyone out there tried modifying the firmware? Do we know if it differs from standard Sailfish, and if so how? Do we know what it takes to compile and load it?

Hmm, well if you are using a slicer that lets you add start and end g-code. It's really simple.
Unfortunately flashprint doesn't.

Simplify3d does.

Also doesn't the firmware actually let you keep heaters on after a print - pretty sure I've seen it as an option from the control panel.

what are you actually wanting to do ?