Now Im going to ask a stupid question. It has not changed since the mouth opened up, still eating. Should I try to push the mouth back in? Gently obviously. I mean its not looking worse, just not sure if some freak reason happened like a frag dropped on it and it can't spit it out or something. Racking my brain on this issue over here.
What exactly were your "sky high nitrates"?
For example, lets say that NO3 was 60ppm, a 5gal (12.5% of 40gal) water change would have only brought NO3 down to ~52.5ppm, then the subsequent first 15gal change would have brought to ~32.8ppm, then the second 15gal change would have brought to ~20.5ppm.
The above assumes that no new nitrates were being added to the water column during the time period of the water changes, but that is probably not the case... so the net net is actually probably(?) a bit higher than ~20.5ppm even after the water changes.
5gal of 40gal - 12.5% of 60.0ppm NO3 = ~7.5ppm NO3 removed
15gal of 40gal - 37.5% of 52.5ppm NO3 = ~19.7ppm NO3 removed
15gal of 40gal - 37.5% of 32.8ppm NO3 = ~12.3ppm NO3 removed
Obviously don't know what your starting NO3 is/was, but I say keep with the water changes... just realize that your same 15gal change (37.5% of your 40gal) removes less and less total NO3 with each subsequent change as the total NO3 number comes down... so it takes quite a few partial changes to lower total nutrients in the water column.
Since it sounds like you've gotten a build up of NO3 over time, you probably have a nitrate factory somewhere in the system (excess detritus, decaying food, etc)... I used to use the round "bio balls" in a trickle filter in my sumps and determined that they were a NO3 factory... removed. Other areas are sand bed, live rock crevices, etc.
Hope your Haddy recovers!
eta: Oh, and although I am no nem expert by any standard (have a couple BTAs and one Haddy myself), I personally would not try to push the mouth back in on any nem... I would think you're more likely to increase the stress level than anything else by doing so.