Can I Add Extras (YouTube Money, Cover Song Licensing, Etc.) After I've Uploaded My Release?

No.

You need to specify all extras when you upload your album or single to DistroKid. 

If you want to add extras to a release that's already uploaded, just delete it and re-upload (but select the extras this time).

The time it takes stores to delete is roughly the same time it takes them to add. So you won't have too much overlap (or gap) between both versions of the release.