The user that creates a policy is the assigned owner of that policy. You must have the correct permissions to edit a policy you don't own.
You can't use a policy owned by a different user, but you can duplicate the policy, then use the duplicate. Duplicating policies prevents unexpected policy changes from affecting your network. If you assign a policy that you don't own, and the owner modifies the policy, all systems that were assigned the policy receive the modifications.
You can specify multiple users as owners of a single policy.