strongly against.
New specialization is legitimate change in character developement. ie. Sooner, using SMG in close combat. Later he gets to plains and needed long range weapon, and after some time of use he respecializes for Assault riffle.
Survival in the jungle, who become tired of beasts and wilderness, relocates to Seattle. Soon hhe find his skill usefull in new are, and since living in urban has some specifics, he changes specialization from Jungle to Urban
I dont see why even ask GM for approval of something like this.