Update from RC to Stable, or need to reinstall Stable when available?

[stevef]

If I install Linux Lite 6.6 RC1 now, can the system be simply updated from the installed RC1 to the Stable version when it's ready?

No, RC versions are stand alone releases for testing.  There is no in-series path to them or from them.
Only install RC if you want to help with the testing.

If you install the current stable version 6.4 there will be an in-series upgrade path to 6.6 Final when it is released.
If the system is remote, best to let other people try it and report back before getting your friend to go for it.