I understand your concern. A notes on this:
When you open an older Test Project with a newer version you'll be asked whether you want to upgrade the project. If you choose "Yes" you'll no longer be able to open the project with the older version. However a copy of the project is stored as back-up under ProjectFulder\backup
It's definitely recommended that you keep all your Test Studio/RunTime instances in synch in terms of version number.
Here's what I recommend: install the Latest Internal Build on a separate machine but don't activate it. When you need to use it temporarily deactivate one of your "normal" Test Studio instances. You can use the newly-released license to activate the Latest Internal Build located on a different machine. When you're done working with the LIB instance, deactivate it and migrate the license to the original machine. That way you don't need 2 separate licenses. Check out this KB:
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