So still persistent and trying to get unused units to work like normal units would, unused units use the scout grp file so how do I use my own grp file without editing another unit's grp file?

That makes the solution a bit more complicated. Honestly, the easiest way is to just replace an existing unit's GRP file and use that; but if you're determined not to, you can try messing around with adding new entries in arr\images.tbl, linking them to a corresponding images.dat entry, linking that to a sprite, linking the sprite to a flingy, and linking the flingy to your desired unit's graphics.

Sorry for late reply but my goal was to revive unused units and make it multiplayer compatible but have maps exclusive to my mod