Since you said that you're open for asks about your reinterpretation of mutant apocalypse, what is a major thing that you will change? If you don't mind me asking . But if that reveals too much about what you're planning, will chumpy be the same as in Canon?
Short answer: a lot. Longer answer: Mutant Apocalypse has a lot of cool ideas it abandons, so it can focus on being boring. I hope to 1) explore some of the ideas it brings up, like Donbot, Maximus Kong, and how the hell the mutagen bomb exists in the first place, while 2) connecting the story more to the characters and how their time in the apocalypse has changed them.
For a more direct answer, the story takes place in New York, which is now in Maximus Kong's iron grip. Raph and Donnie haven't set foot inside the city since they failed to stop the mutagen bomb. But when Mira convinces them to help her find her brother, who was taken by Maximus Kong's forces years ago, they find themselves back at the spot of their greatest failure. In this ruined city, there are as many ghosts haunting the brothers as there are new hopes blossoming. The entire plot is getting replaced, along with some major character differences and additions. And yes, Chompy is going to be the same. No point in changing perfection :)