There are some other options, but at a glance, the second line above sounds like the right direction for your question? There's a few gotchas with it as well, but I won't waffle about those unless you confirm the basic idea sounds right for you.
you can set workflow properties.
so for example a property for an issue that is in state "closed" could look like:
nobody can edit the issue after it moved to "closed"
i personally use this:
so only users that are included in this projectrole are able to edit
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