Field not updateable but updates when header changes

I am not sure if this is possible through forms personalization or not.  I would like to have vendor sites where the terms code is not enterable (this I have already accomplished) However, if the terms  on the vendor header record are changed, I would like to have that change occur to all sites for that vendor. This is the piece I am not sure how to accomplish.  Any help and direction you can give would be greatly appreciated.  

apps 11.5.10.2