Comment # 1 on bug 1120838 from Thorsten Kukuk

Either you do (In reply to William Brown from comment #0)

> I'm not quite sure if the mistake is in my process of the repo addition, or
> an issue with transactional-update itself handling additional repos.

zypper ref of course is not allowed to write to a read-only root filesystem.
No clue why you think it is necessary at all.

Either update the package manual and accept the key manual, or use
auto-acceptance of the new keys.