I think this answers my basic question. This looks like it may be new material in RawPedia because I thought I was pretty well read on processing profiles. The first sentence says, “Processing profiles evolve from one version of RawTherapee to the next. We strive to ensure backward compatibility (e.g. a profile created in 5.3 and opened in 5.4 should look the same), but this is not always possible.”. I take this to mean “go ahead and try it but you can’t count on it to produce the same result.”. With respect to workflow, my interpretation is that if you want to preserve the state of the editing that has been done in a manner that either editing could be resumed from that point or additional exports made of the same result then you had better retain both the relevant processing profile and the version of RT used to create it. Based on this experiment & discussion I’m also inclined to think that one should be sure to make (i.e., save) any processing profile that is to be preserved in a way that RT will not confuse it for the ones that are automatically opened & rewritten without requesting user permission.
That leads to the question, “might it be better to export the resulting image to a file using a standard format that could then be reopened in either RT or any other image processing software?”. I think this would eliminate future ability to perform certain raw processing operations such as demosaicing. I’m not experienced enough to have an opinion about this but would be grateful to learn form those who are.
Of course the answer could also be to take both of the above actions.