Depends. If you can simply turn the game from non-adult into adult, chances are it might already be aimed at adults. So why bother having two versions. You could provide the patch on the same project page and have that marked nsfw.
If your game aims at children, there might be something dubious about the concept, if you can turn it into an adult game with a patch. Also, you might want to release the family friendly version on a separate account. Kids would check out your profile and see the adult version. The account setting on adult content does not work for profiles. It only works for browse and search.
Also, are we talking adult adult or adult as in scary horror games. Like, do you change the game from bikini and hugs to no swimwear and some more hugs, or do you change implied violence to blood splatter? For the first, consider making it nsfw regardless. And for the second, check if you would even need the nsfw marking.