It appears this is not possible for FrostWire. The program is hard-coded to create a special file called hostiles.dat that forces the program to check the hash of the hostiles, if it does not match the one downloaded then it will re-download it (via torrent) & replace the one you put into place. The hostiles FrostWire would download has not been updated for some years (not sure how many years, perhaps between 4 to 5.)
Edit: it appears the hostiles torrent has now become inactive, which means you are left with zero hostiles.
I can't remember when FW started using this approach but the hostiles should work with the earlier versions. I did test this some years ago but cannot recall the latest FW version a standard hostiles file can be used.

Using any of the hostiles I linked to above should definitely put less load on the FW program.

Phex? I've never been able to get the hostiles (even the BearShare version) to work with Phex, though a few years ago GregorK said it was possible.