You can also switch to "Add New Clothes" mode which is effectively a clothing store where you can buy whatever you have unlocked. One factor which will advance what you have unlocked is your Fashionista Level. Fashionista Level will advance as you spend time in the Clothing Customization Terminal. Some clothes will remain locked, presumably unlocked by other advancement methods.
Individual articles of clothing can be modified by color or with decals and symbols. Any decal or symbol can be modified as well, rotated, resized, stretched in any number of directions and repositioned to your liking.
When you modify a piece of clothing, it stays that way. You can not buy one shirt and have 15 different patterns. You must buy a new shirt (thus owning 2) and modify that one as well.
You can trade articles of clothing to other players (a handy way to distribute a uniform, if your friends are going that direction) by duplicating them in your locker (L). Choose the item. Edit it. Duplicate it. Refurbish it (this makes it tradeable). Typically the cost associated with duplication is slightly higher than the cost of the item being duplicated.