I'm gonna be real honest here, navigating through the missions via changing the savefile is both a bad idea and very difficult to do 9because it's a bad idea). Worst case scenario you'll break progression. Best case scenario you'll softlock the game.
The save file tweaks are more meant to unlock specific galleries, add lewd arcana or lewd blooms, unlock and levelup specific items, that kinda stuff. Soft cheat codes, if you prefer.