After changing settings in Preferences - movies still loading to OS drive

I have a new computer and wanted to move my movies to it. I went to the Advanced setting in preferences and changed the path I to what I wanted. When iTunes came up or course some movies had to be reloaded but some did not show up so I copied from my old computer. I opened each folder to the movies and used 'Open with' in Windows to play the movies. This created or had the movie in my list of movies. Now it seems that I have to go to the 'Edit Preferences' each time I open iTunes to keep this path available?? But when I purchase a new movie iTunes downloads to the same NORMAL iTunes path and is filling up my 'OS' drive with the new purchases?? Can this be made permanent to some degree or am I just stuck with movies filling up my system disk and I have to manually move them to the disk with my movies?