I believe it is possible to invisibly repair cracked ABS bumpers using the hot staple technique and a suitable filler. If the repaired bumper is to be painted I see no reason why a proper repair couldn't be made. You may need to talk to the folk who repair motorcycle fairings rather than car people tho'.
Certainly the staple repair a friend did on the cracked rear hugger on my Yamaha GTS1000 is unobtrusive even without final filling and refinishing.
Its impossible to remove the ABS from the metal support frame. If you do resort to another bumper or even if you just pull yours off for repair its advisable to seriously de-rest and proof the metalwork. Mine was OK but not pristine when I pulled it off to fit parking sensors shortly after buying the car. 11 years on when I pulled it off again to replace the parking kit due to a failed sensor I discovered the mounting lugs had disappeared and the rest of the support was in a bad way. It was basically just sitting there. No way could it be refitted as was and, being unwilling to trust pictures to be sure of getting a good one mail order, I resorted to creative welding and re-engineering of brackets to span the missing parts of the metalwork. Had to make a couple of special alignment tools to get the new brackets in the right place. Took 4 days of on and off work due to the essential breaks to bring my temper back into acceptable human range. Welding to (mostly) rust is not my favourite pastime. Considerable verbal encouragement was involved!
Having put it back on it looks pretty decent actually and lines up perfectly.
Seriously annoyed with myself for not taking the time to treat it properly when it first became apparent that my car suffers from rust overt the alst couple of ft of chassis et al. As it was once a seaside care I suspect it may have put boats in the water a few times.