Stop iTunes writing tags on import

Hi all

I have an issue with iTunes that maybe someone can help with. I have a lot of mp4 video files that I like to tag as TV shows indeed some are TV shows I've taped off the TV. Any how the files have had there meta tags set to TV shows and part or a compilation set to yes and all showed up in the TV shows section of iTunes. Now every now and again I do a clean install of the system or copy the shows from my main mac to the tvs Mac mini and when I re import the files to iTunes , iTunes then converts all the files to home movies and sets the part of a compilation back to no. All others tags remain unchanged. The biggest problem about this is that I use retrospect as a secondary backup solution and as iTunes has modified the files it wants to back up all 200gb again

Is there a way to stop iTunes editing tags. On import.

Cheers

Steve