Costumes are made in the launcher, they are only updated later through NPC, so this is where my suggestions belong.
1) An Undo button.
This is the most obvious: costume creation needs an Undo button. Currently there are buttons all over the screen for resetting parts of costumes - certainly to be avoided, because if you have been matching patterns and colors on the upper torso for the last six hours, you won't want to reset it to Tight. The reset button for reverting to the previous random costume is even more dangerous, because there is no button for moving to the NEXT costume in queue. Hit that by accident, and all your work evaporates in a cloud of smoke. As a result the screen is a minefield, and I have to be much too careful clicking around it.
2) Pattern and fashion choices in alphabetical order.
It doesn't take cutting cloth for long in the costume editor to learn what the different options stand for: what the Overguard pieces are, what the Imperial Dynasty, what the Psych, Magic, Alpha patterns look like. But it takes a hell of a memory to remember in what order they stand. The patterns are always the same, thank goodness, and it's alphabetical, but the elements are either in the order of appearing in different game updates and expansion or simply at random. I remember I liked Goldbricker, where is it? The old sequence doesn't matter: all of the options are available to all players now, nothing is locked away or premium. So arrange this in a simple manner.
3) Looking at gloves makes flickers appear.
When I scroll through glove options and maybe some of the other smaller body pieces, often glowing balls float up from the bottom, as if an aura were on. But it's off. They obscure the view.
4) Costume edting at login for existing characters.
When I select a character to proceed to the server, show a button for customization here by the by. Rearranging a costume is free in-game, all it takes is talking to the right NPC. Why not show a shortcut here?