Yes usually the Atari and Commodore users didn't get along very well. Competing platforms. The Atari had more colors and a more advanced BASIC, but the Commodore had more tricks to it and an add-on Simon's BASIC. I remember a local group, The Wacko Cracko Brothers, modified C64s, they added more RAM, and updated the ROM to use a more advanced BASIC and RAM switching abilities to use 64K banks of RAM.

I also remember modifying a few "Compute!" games for the C64, so that Balloon Blitz became Klingon Blitz and I turned the Balloon into a Klingon Bird of Prey.