Here some ideas for people who want to save slots :
1. I remove all duplicated costumes of original game and fuse them into one with hairstyles method with LNK Reshuffle. (see Mralex previous post)
Example : Phase 4 Black Hooded Cloak, White & Red (2 Slots saved)
2. I replaced those 2 slots with others mods.
Example : Due to the fact that my previous example were with hats, I used others mods that come with that feature and/or toggleable
I have ported Ayane C31 Pink Overalls + White Ski Cap costume to Phase 4 to be at the position of the "white hooded cloak" costume.
3. To save more slots I can add others mods that are similar like recolors one and/or nude parts of them into the original one (same way as n°1)
4. If you really want to optimize more and more, the h & hl method can be usefull, but sadly I am not good at all to do it, so I encourage community to fuse costumes alternatives with this method if you can.
5. I wish TN will do something one day to unlock more slots specially for VF characters cause they are too much limited.
Tip 1 : when I have mods with a wrong P icon I try to use them to replace those original costumes that you can't change P icon so they are hidding behind. I leave the mods with right P icon with DLC Tools method
Tip 2 : I even fuse those duplicate costumes even if they belong to others characters
Example : like those made at base for Phase 4 with another color, so I move them to Kasumi.
Tip 3 : Sometimes I have noticed that for the same slot, two players can choose the same character costume slot as condition they just choose another hair that give a new costume.