Unless the file is a specially made file, I don’t see the necessity
of resharpening files.
Files are a consumable, just like saw blades. The time spent &
materials used to resharpen the file will exceed the cost of
replacing the file.
The trick to prolonging file life is proper use & care. Use a file
card to clean the teeth if they get gung in them. If that won’t work
use a scriber to push the stuff out.
When storing the files store them sot the file teeth don’t bump into
the teeth of another file. Usually storing them vertically in a piece
of wood with holes drilled in it to fit the tangs of the files works