Can a mod please clarify why this answer would not qualify to be deleted (and instead should have been posted as a comment.)
This is literally the posted answer ( see here: How to Rename Theme Folder in magento2)
Follow above step
Give Write recursive permission to Design folder
The answer just references the post above, which one who knows? and I got banned for raising flags for 7 days for raising the flag 2 times. Seems a little extreme for something that IMO isnt an answer, nor does the OP think so and someone else in the comments.