According to BioWare, modifying the Coalesced won't result in a ban as long as it doesn't lead to an unfair advantage in multiplayer. I've heard that BioWare no longer bans cheaters in multiplayer anyway, so you're probably safe.
I'll try that fix myself. The HUD size has been bothering me for a while. I once sent a private message to former BioWare employee Chris Priestly, and he acknowledged the issue, but said it was low priority.
Edit: This didn't work. I tried several values and even tried setting DesignerHUD to False, but my HUD is still the same size.