Is there a way to play the game again completely fresh, with no armor abilities or weapon attachments already unlocked (after beating the game once already)?

I don't think you can. There was a glitch that if you started a new game on a different difficulty setting the game would treat you as you're playing it for the first time, but I'm not sure if that was fixed or not.

Uninstall and reinstall if you're playing on PC, or maybe you can delete the game from your Xbox / PS3 hard drive?

If playing on the xbox or ps3, you can try what I've done with some games which is just use a 2nd/guest account & play through it again. That or just delete the saves but no telling what is tied to the multiplayer with trying that.

Yeah I figured as much...that's unfortunate :( Thanks for the help though, I've posted this on so many different websites and this forum is the only one where people gave actual advice lol.

Nope guess you'll have to wipe the save