No, though I would recommend Notepad instead of Wordpad. Personally I use the completely free Notepad++ for maintaining all of the data files used by GCA.
The reason why you got the permission denied warning is because you were trying to save it back in the Program Files\GURPS Character Assistant 4\ folder. By default newer versions of Windows does not allow users to save, modify, or edit files in those directories without elevated permission. You should be able to save in the Documents\GURPS Character Assistant 4\data files\ folder and the data files you've saved will be made available in GCA4 with a slightly different color hightlighting in the Data Sets window.
There is a lot more information in the GCA FAQ
post 12 and
post 13