Yes. Although I would recommend having the cable at hand in case of unexpected issues. The header is already soldered on the ZyXELs.
The realtek target is very new, and test coverage is relative to the total number of users over time. You can easily end up doing something which has never been tried before. The support in 21.02 is limited for the same reason. Both devices and features have been added after the branching. You might be better off with a snapshot/master image.