cautious update of variables – best approach?

So ... I have a stack of user variables, some of which keep the same value in every chapter while others are manually adjusted. File > Import formats from a "good" file will trample on the manual variables in the others. Short of setting up a quick todelete.fm with just the one user variable I want to flood through the book, is there an easy way of updating just one? I suspect "plugin" may be the answer <g>