Yes, closing the program and restarting it. The changes should meld into any existing campaign/career.
So, I tried doing the same thing that was discussed in the forum, but didn't have any success getting Blacklisted mechs to spawn. After doing some more digging, I was able to find another old thread on this forum (that I can't seem to link to because I haven't posted enough, and was an old enough thread that I figured I shouldn't necro it) that said that I also had to edit the metadatadatabase.db file, removing the Blacklisted tag in there as well as the .json files. After doing as suggested I was able to get the Blacklisted mechs to start spawning. Man, gauss rifles are a lot less fun when they're being shot at you
Anyhow, my only problem now is that I'd like to be able to salvage advanced equipment (er PPC++, double heat sinks, etc). I've removed the Blacklisted tags from them in the .json files, but I can't find a part of the metadatadatabase.db file that references them. Does anybody have any suggestions?
I created a MOD which you can use HBS Mod Loader to use if you want it. It also removes blacklist tag from DLC mechs (if you own the DLC).