potentially dumb question, but it it possible to rename internal ids of custom record and/or custom record fields via SDF? seems like this is not possible from my attempt since it cannot reconcile that the update applies to the same-id field, even if in same order since the id has changed

I think you're correct, you won't be able to update in the XML document, but you should be able to login through the IDE and update the script ID that way? I'm sure the idea would be to avoid logging into the account though.

correct, I was guessing that was the only workaround - having to first update the relevant ids in the account UI manually in order to get everything to map correctly, just wanted to confirm there was no alternative purely through SDF