I would advise against it. The destruction of a good friendship is not worth it.
I'm really ticklish, and tbh I've had a secret weird desire to be tickled all over my bare stomach. Is it okay to ask my really close best friend if she would do it? I trust her and know she always listens to me and never judges, but is it okay?
Can't you reach your own stomach? Then you won't have to bring any oddness into your friendship.