Chris, if I'm following you correctly, you have a GEDCOM file of your own tree, and you know that one or more of your ancestors has already been profiled on WikiTree. I think the preferred approach in that case would be to download your GEDCOM without including the people who are already here, and then work on making the appropriate connections later. The other possibility is to download the duplicates, and then merge them with the existing profiles.
But the implication of the question is that you apparently have a family member or distant cousin who is already active here (or has been). So either way, sooner or later, the situation requires you to collaborate with the other member to make sure that the end result is one profile per person, and the descendants agree that the data in it is correct. Most members would not object to adding you to the trusted list of profiles for which you are also a legitimate descendant.
If I'm missing the boat on your question, please post again.