Guild Wars 2

Are there costum weapon skins that i could apply to for example a greatsword while leveling. and re-use it for a new greatsword after i leveld up?

The only greatsword skin that is reusable is the Fellblade skin from Hall of Monument. The only other greatsword skin is the Greatsaw Greatsword, which is quite expensive and can only be used once, have to use transmutation stones for further uses. What I would suggest is to find a low level or a cheap greatsword with an appearance you like and use transmutation stones to keep the model/appearance every 5 to 10 levels when you switch to new weapon.

Here’s a greatsword gallery by Dulfy: http://dulfy.net/2012/11/07/gw2-greatsword-skin-gallery/

Or, if I understand your intent correctly, you could use a high level one you like, transmute it onto your current weapon, then keep transmuting that to new greatswords as you acquire them. Remember that transmuting turns two weapons into one weapon, you do not keep the old one.