WarpMyMind

Some of my older pay files no longer meet my present day production standards... if I just upload a replacement on the existing file will the new version be available to users who've already paid?

Yes, if you upload a newer version of a file to replace an existing one anyone that has already purchased it will have full access. If you don't want this to happen upload the new version and disable the old on so that anyone that purchased it will still have access but it will no longer be listed as available on the website.

good job on improving your standards and your work!
I have done this before