Have you placed the addon files in the addon folder? I believe the option to enable the extension/addon/mod is available if you place the folder in the Arma 3 folder but will not actually work unless you copy the addon files (the .pbo and .bisign files) into the addon folder. I haven't had the game for very long so I'm not sure if that's correct, but that's what I do and mine work fine. 
As for the registry problem, I'm afraid I can't help you with that one. No idea. 
Hope this helped in any way :cool: