I would like to know if there is no way to customize the character and leave "forever" I had won the item that lets me choose a character that will be at lvl.60,however it does not let me customize, it already comes with a normal appearance, and I would like to know if there is only this coupon that gives me the chance to customize for only 7 days and then it goes back to how it was before, it doesn't pay much.

Yeah but just merv's palette, character changes are forever

Character customizations are permanent unless you change it again. The 7 day coupon will allow you to customize any of your character within that duration. After it expires, it won't revert back to your old look. So meaning, you will retain the changes you made.

TIP: Save your favorite customizations you've created in Beauty Album. This will allow you to change your appearance instantly as easy as changing costumes, whenever you have an appearance coupon. You have an option to either share or keep those customizations private.