It's all wrote in the title.
If we can customize some object like a mask or a hat or every things like that,
That may had a lot of more diversity skins !
And in my opinion, that may be simple to incorporate it to the game

I don't think I get what you are suggesting, customize how? Just the texture? Because we already have some items where you can do that.

http://forum.toribash.com/showthread.php?t=572696

This is only available when you pay with real money
The stuff that I'm talking about is reachable to everyone (like kids or skinflint [me])
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Yeah just the textures,
Imagine that you want to put your profil's logo hat in-game,
Then you'll buy the hat in-game and then add the colors and the drawing just like a body texture

As WeppetKo said, there already are some texturable items. I have two, you can check my deac.

fyi, these following 3d item can be texturized (may or may not be 100% accurate)
1. Valk wing
2. Anime hair ( i heard it can be texturized, i may be wrong tho)
3. Sport headband

Not only the valk wings, but all of the valkyrie items are texturable.

So is the body pillow, umbrella thingy