I'm migrating applications from a release automation 6.3 installation to a new installation with version 6.5 Is it possible to export and import users, permissions and groups as well so that I do not have to create them again?
Upgrading on same box is supported way to keep user info. I don't know the steps to move user/group/permission to another server.
I have not verified, but the combination of REST APIs may help you. You can check the Administration APIs here.
However, we don't have further documents for these APIs at this stage. Additionally, I suppose you may need to edit JSON gotten using API manually before importing.
So, if you can create again, I recommend to do that.