Une question qui peut paraître un peu bizarre ^^

Everyone is permitted to copy and distribute verbatim copies of this license document, but changing it is not allowed.

Traduction : tout le monde est autorisé à copier et distribuer des copies de la licence, mais aucune modification n'est autorisé.

Pire, si tu retire la licence et que tu t'amuses à modifier, si un jour ça se sait tu peux risquer gros je pense.
Maintenant que je sais ce que tu veux faire, je vais te faire du chantage pour que tu me donnes de l'argent afin que je me taise mouhahahahaha :D

Le point #5 de ton lien est plutôt explicite (et de toute facon c'est relativement connu): tu ne peux pas.
Si tu te sers d'un code sous GPL, même modifié, tu dois indiquer sa provenance dans l'interface utilisateur.

5. Conveying Modified Source Versions.
   You may convey a work based on the Program, or the modifications to produce it from the Program, in the form of source code under the terms of section 4, provided that you also meet all of these conditions:
   a) The work must carry prominent notices stating that you modified it, and giving a relevant date.
   b) The work must carry prominent notices stating that it is released under this License and any conditions added under section 7. This requirement modifies the requirement in section 4 to “keep intact all notices”.
   c) You must license the entire work, as a whole, under this License to anyone who comes into possession of a copy. This License will therefore apply, along with any applicable section 7 additional terms, to the whole of the work, and all its parts, regardless of how they are packaged. This License gives no permission to license the work in any other way, but it does not invalidate such permission if you have separately received it.
   d) <u>If the work has interactive user interfaces, each must display Appropriate Legal Notices</u>; however, if the Program has interactive interfaces that do not display Appropriate Legal Notices, your work need not make them do so.

Merci encore :)