You should probably use a completely separate Google Account than the one you ordinarily use for uploading this extension. The webstore does show other apps created by the same author, so if you were to upload multiple extensions from the same account, and it was known who created the other extensions, that would be one way to tie it back to you. The other things that could tie an extension back to you are the contents of the extension (e.g. if you had your own personally identifying information in the HTML or JavaScript embedded in the extension code). Another way that they could attempt to unmask you is by sending an email with a virus to this account (the webstore does provide a way to contact the extension's author, I believe).
Google does comply with valid legal requests. Interestingly, Google's Transparency report doesn't seem to show any data on requests for user data from Ukraine. I doubt that, faced with a request to de-anonymize a dissident who has otherwise done nothing wrong, that Google would comply. That being said, as a political dissident, it's always better to be safe than sorry. For making the registration payment, you might want to use MaskMe or a similar masking service. You might also want to use a VPN for all of this so that all your activities (both encrypted and not) occur outside of Ukraine.
Anyway, that is a very interesting question, and I wish you the best of luck in restoring santity and democracy over in that part of the world.