It has the possibility to mess things up, yes, but it generally shouldn't as long as the pack you're using has all of the sounds in its own folder and so forth. Any plugins it has that it may want you to install, MUSHz probably already has, so its best to not mess with that unless the new pack doesn't work. I honestly don't believe in working that way, so I don't know much about it, you might have to deglobalize certain plugins and add them to altar. Really its just best to get mushclient separate from mushz and copy all the plugins in and go from a clean slate, but whenever I say that, people act like I'm speaking in tongues, so try it if you want, just don't be surprised if you run into problems.