Rewriting immutable commits is only "fundermental" if it's enforced upstream. You can always break the rule locally.

That said, jj will warn you if you try to edit an immutable commits, and you can configure what it considers immutable.

There's a configurable setting for which changes are marked as immutable. The default works perfectly for my workflow (pull-only from upstream, rewrite and push freely to my fork). other workflows may presumably need to tweak it

https://www.jj-vcs.dev/latest/config/#set-of-immutable-commi...

Don't rewrite shared public history

It's ok to force-push a branch that only you have worked on (and even in the case of others working on the same branch it can be fine as long as you communicate with them)

Jujutsu is immutable for public changes by default.

You can force changes with a ‘—ignore-inmutable’ flag.