I would only file the spurs slightly to make then NOT SHARP. You cant file them too much to shorten them. You could go too far and cause bleeding. Don't know what you would have to do at that point,,,,
Just use your people nail file or emery board.
WISHING YOU BEST,,,,,
I use a large heavy duty dog nail trimmer to shorten the spurs, and then a file to smooth the cut surface. It's best to have two people; one to hold, and one to trim, a bit at a time, to avoid the quick.
A hack saw blade like one uses to cut metal works well. A small ball of old beeswax to saw into before cutting begins on the spur is a good way to prevent or reduce bleeding if you cut into the quick. Re-wax the blade about 1/2 way through cutting the spur. Any way it is highly unlikely that a rooster will harm a hen when treading her. A bar of soap is also good instead of using beeswax.