Yes, there is a new ISO on the way.
However, since Netrunner Rolling, as the name suggests, is a rolling release, there is not really any reason to ever have to reinstall.
Now to answer your first question, yes it is safe to remove firefox and replace it with firefox-kde-opensuse.
I’m the maintainer of the firefox-kde-opensuse package, it provides firefox, compiled using the same options, and compiler as upstream arch, the only difference is my package is patched for plasma, as well use of global menus.
Regarding the reinstalling of a rolling release:
After almost two years I have collected a couple of what I guess is AUR related problems I thought it would be nice with a clean start.