You won’t need to reinstall again, once you’ve set it to gts you’ll stay on whatever the -1 release of Fedora is automatically. I set all my work machines on gts.
So you’ll get upgraded to F39 when F40 comes out. What happens is on release day we update the latest and gts tags to point to the new values and then our computers will all follow along.
- More info here: Bluefin Administrator's Guide