Does mozilla allow to modify the core strings in it.

Is it possible to add an extra variable to mozilla string(nsTStringRepr). I added a bool variable to nsTStringRepr class in Xpcom/Strings/ While building the build I got static Assertions like below /Users/pavan-6853/Desktop/MOZB

Does mozilla allow modification of Strings

Is it possible to add an extra variable to mozilla string(nsTStringRepr). I added a bool variable to nsTStringRepr class in Xpcom/Strings/ While building the build I got static Assertions like below /User/Desktop/MOZ