You MAY be able to switch without adding a shim. It depends on how you are operating the engine and how closely it was shimmed before. In other words, if your engine is shimmed a bit on the + side for 20%, it would probably be OK on 30. You can inspect the piston and chamber after a few minutes run time. If it is nice and shiny, it's all good. If it is begging to dull, it's time to add a shim. You could just add one to be on the safe side, with little loss of power.
The shims are not brand specific. They are interchangeable between engines with the same bore.