I did an experiment, I used the find and replace function available in MS Access, and I was surprised to see that it actually interprets the hash as any number. Although being annoying in this particular case, that if you want to change the hash to something else you can't, it may be a useful feature if you want to search for numbers in a field. However I'm not too sure about that, because it only seemed to work in a number field, and not in a text field. If that's the case I can't really see the point! Maybe it's not a feature, just some sort of bug.
Anyway, the attached file contains a simple routine to replace the hash character with a "C".