Unfortunately, HI-TECH doesn't do any removal of assembly language routines. It either links in a whole .asm file or it doesn't.
Another way you can accomplish what you want is by adding your own source .asm file. You can cut and paste only the routines and code you want from the library .asm file (and any needed .inc or .h files). You could change the names of each of the routines in the same way. Then, your calls to the routines will only go to your custom file, and there will be no calls to routines in your library .asm file. Then, the library .asm file won't get linked in at all, whereas your customer .asm file will. Now, you're only linking in exactly the routines you want. This may be slightly tedious, but it should work fine. You also wouldn't need to worry about trusting someone else's perl script