Question on Unrecognized BGP Path Attribute

Hi, I have a question about unrecognized BGP path attribute. According to RFC4271, when a BGP router sees an UPDATE with an unrecognized optional and transitive path attribute, it should retain the attribute, and if the path is selected, it should propagate the attribute to its neighbors. My question is, if later the router sees an update to the path in which only the unrecognized attribute has changed, should it immediately propagate the change to its neighbors? My guess is a yes, but I'm not sure because it's not explicitly written down in the RFC. Another question is, in such a case, what will the current routers from different vendors do? Anyone has any experience on this? Best Regards, Xin Liu