I've separated the NSFW tiers from the original tiers because I know some would rather not see NSFW and vice versa :)
Everyone is AUTOMATICALLY set to the PURE tier (non-NSFW) and if you'd like to switch tiers, just choose the "UNPURE" version of your tier. There is no price change/difference for the added NSFW tag.
In the image, I've circled with an red outline the changes.
A guide to switch tiers: https://support.patreon.com/hc/en-us/articles/360000126286-Update-my-membership-amount