Nope, just the code in the mod proper. Feel free to take a crack at this if you like.
I've started poking around at this. The good news is that the HUD edit is pretty simple, but I found out why changing the movement code is a headache: it's copy-pasted across every weapon. I guess the Deimos-1 dev didn't know about using inheritance. I'll try to keep you posted, but I started poking around way too late in the day to be doing a full refactor, and I don't wanna half-ass it.
Status update: I un-spaghettied the movement code a bit. As I suspected, the differences in movement between weapons is encoded in the copy-pasted movement code, and I haven't adjusted for this yet, so right now everything handles as if it's the pistol. I'll poke at it a bit more. I could probably zscript-ify a lot of it, make it easier to alter the movement properties.
[EDIT]: Also, I tried putting together an upgrade item for the handgun. Since you suggested replacing the handgun entirely with the SMG, I figured, why not just make the "SMG" a full-auto conversion kit for the handgun? It fires every 2 tics, which is slightly faster than the AR (which fires every 3 tics). I might try upping the mag size as well later, but right now it feels pretty good.
All right, I've got a working version. Handgun upgrade kit doesn't spawn yet, use `summon HandgunUpgrade` to spawn it for testing. The weapon movements are jerkier because of how I redid the movement code, but I think I know how to fix that; I just wanted to upload what I have rn so you can poke at it. I've uploaded it to MediaFire here.