OK, after reading Fred's last answer on the other question, I think I might know what you mean.
I think you're asking about uploading a new small gedcom and whether that will overwrite profiles created from a previous gedcom upload.
First, see http://www.wikitree.com/wiki/GEDCOM_FAQ#After_importing_a_GEDCOM.2C_can_you_update_your_profiles_with_a_new_GEDCOM.3F
The profiles in a new gedcom upload won't automatically overwrite anything, but they'll need to be merged if there are duplicates. If there aren't very many duplicates (because it's a small partial gedcom of mainly new people, which I think it what Fred was recommending) then this is no problem. If it's hundreds of duplicates, that's going to be way too much work.