Associating file extensions with separate programs for XML files.

Hello! I have two files that are both XML files, according to the properties tab. One is named one.tks, the other two.pvd. I've tried associating both files to different programs, but since they are both XML files changing the default program for one.tks will also change the default program for two.pvd. How do I associate the two different extensions (tks and pvd) with two separate programs?

Many thanks in advance!