The reason you are advised to start an initial Play Now game is not to clear the cache, but to clear saved options. This is ONLY an issue if you are switching to RifE from another mod (or another mod from RifE, or one mod from another in general), as saved options are saved by position, not name. Causes issues with hidden options.
Loading a save will not work; You must actually start a game in order to clear saved options. Next version of the launcher will have an ini backup feature, which can be used rather than starting a play now game, aside from the initial time.
Basically: Run a play now game, exit the game, open up the launcher, hit 'edit ini', hit the box to backup your ini, and then you're good. Next time you switch back to RifE from another mod, simply open the launcher, hit 'edit ini', and select the 'load from backup' option for the ini file. Since saved options are stored in the ini, they are now wiped.