I checked the standards on negative lookaheads in Javascript, and the way I am laying out the RegEx match string should be correct. I even tested with RegEx buddy, and it matches/doesn't match what I want it to. Yet, OverrideFormats won't attempt to check the negative lookahead. It just skips the lookahead pattern and matches what's after it (.*), which means everything. 
Putting the negative lookahead in the Blacklist doesn't work either. Putting the folder in the whitelist didn't seem to help either. I ended up having to hardcode the negative lookahead in a separate Path Format in DOpus settings, and comment out the line in the whitelist, ^.:\\.* (so that it became //^.:\\.*) to disallow OverrideFormats from processing overrides in other folders, which I didn't want to do... lol.
Wait, so your path function is replacing every slash with two backslashes? I don't know javascript very well, but that's what the function looks like it's doing.
See here, so you know what I am attempting to do, though you may already know... lol.