I've had my PRS SE for about a year and a half now, and after using it as my primary guitar for a while, I've noticed that there is an indentation on my 18th fret on the G string. It could be a defect, but I've just noticed it. Would it be possible for me to file it down, without ruining the fret?
You better ask building/costumization guitar forum on this one. My first guess is that you'll screw the action if you file only one fret.
You wore down the fret playing the same bend repeatedly. This is normal. If the notch is small you can have the frets all filed level. If the notch is big you can just have that fret replaced.