I don't think it is possible. However, it is always fun to be proven wrong
I tried using the regular PUT endpoint for /contents. I changed the author but the change did not persist. Per the documentation: Jive REST API v3.14 → Post entity The "author" field is read-only on edit operations and cannot be changed. I'm not aware of any other author changing endpoints
I tried a similar approach as listed here: Changing the document author using the Jive REST API but could not get it to work either..