If you would simply like for your veneers to have the shape or bite altered, then you should not require anesthesia. By contrast, to completely replace your veneers would require you to be numb as they will have to be taken off with a dental handpiece. Good luck.
Your veneers look really nice and you have a beautiful smile! Just go back and ask your dentist to adjust the length of the veneer that is bothering you so you will be happy with your smile. Your lisp is temporary and often happens when your teeth change shape. You will correct this...
If your dentist offered some type of warranty for his/her work, I would recommend getting dental bonding/white filling done to temporarily cover the problem tooth until you are able to return home to have the veneer replaced. If your dentist did not offer a warranty on the veneer, I would...