Can I do kickboxing with porcelain veneers?

As long as you are wearing the sports mouth guard you can continue with the kickboxing.  This should give you enough protection from damaging your veneers.  

They can be affected as much as your natural teeth, if you receive way to many punches might affect, but if you are not an professional kickboxer, use the mouth guard and you should be fine.

That's a great question, I would treat as if they're your teeth and if you didn't have veneers.  I would highly suggest to have your dentist make you a custom mouth/sports guard.  Good luck!