I was looking around And i saw so few colecovision hacks. Is this an easy platform to modify?
As platforms go, yes, I think it's one of the easiest, along with the near-identical SG-1000. The graphics are in a straightforward format, the Z80 processor is very well-documented, and things like compression are rare if they happen at all. I've been able to translate two SG-1000 games (both of which were ported independently to ColecoVision) with little more than a hex editor, a tile viewer, and a relative search program.
That said, the things you're trying to do require programming skill, and are difficult on any platform. Why not start by trying to hack a game like Dig Dug or Pac-Man to use different sprites, and take it from there?
I'm guessing the program you mean, BTW, is Gateway to Apshai. If you understand assembly language you might be able to look at the Atari or C64 versions and, after considerable effort, duplicate their approach. If you don't understand assembly, it'd be more or less impossible to do the things you ask.