Is there a homebrew application/ sys-module to slow down and speed up gameplay similarly to cheat engine on windows or game guardian on android. I know you could change clock speeds but I don't believe that actually changes the speed a game runs.
No of that I'm aware of. Only way that I know is to change "GetSystemTickFrequency" (only in games that use this function). 19200000 is the result, so cut it in half - you get twice the speed. Multiply by two - you get two times slower output. This can make some games unstable.
So for doing this to be changed whenever you want you would need AM mitm - which for now doesn't exist anywhere.