That’s the approach I tried - but I got errors (sorry cannot remember - grappling with work IT since 5am). I’ll take a rest and try again…perhaps just a misstep.
For a reinstall, you shouldn’t need to import the old rpool at all. Perhaps you’re using it as the place to pull your flake from, or other small bits of config (like host keys), or more extensive data (like user data). In that case you want something like:
zpool import -R /mnt2 -t <old rpool pool id> rpool-old
using the pool id and a temporary name to avoid name and path conflicts.
Of course, once you’ve imported both pools like this, you could also send a full recursive snapshot from old to new pool, depending on how much your preference is ‘reinstallation’ versus ‘rearrangement’.