Thanks for the info. I really didn't want to restart.
You shouldn't have to. From everything I've read opting out only opts you out of THAT mission, not the mission type (despite language that sounds permanent). In my experience, RTS misions aren't offerred with EVERY liberation. Not sure if it's a simple matter of not offering them, or I was too busy picking up dominator equipment and got to the planet too late for it... If you liberate 2-3 systems without getting offered one I'd be shocked.