Possible to add one-off contact to an existing sample?

I'm curious if, after having created a sample from a contact list, I can add individual contacts to the sample. It's easy to do this if I'd like to add contacts to another list, but there doesn't seem to be a way to add them to a sample.
Example use case:
If I have a list of contacts for all US-based companies and create samples for each sales region, what if I want to add a contact that may appear in multiple regions, or maybe I simply forgot one that I wanted to add that may not have met the original sampling criteria? I don't want to try to resample with additional, increasingly confusing logic, just to add one or two more contacts. Is this possible?