I have been reading that this tool can do it http://www.sno.phy.queensu.ca/~phil/exiftool/ but damn I dont feel that much doing command line again.
Ideally Xnview would get the tag from the .cpi and then be able to rename both .cpi and .mts (or whatever is video format), and it would be perfect if it could do that either with both files in the same directory or in their official one.