It really depends on the food you're feeding.Pet store WW would be hybrids so they'd need a diet which cannot really be provided from foods available directly in the US,as you'd have to actually go through Viovet for example and get Burgess' dwarf food to get something suitable
Considering it is pretty much impossible that a pet store would be doing that and the foods generally used in pet stores are either unsafe or unsuitable,you're much better off just avoiding a transition as long as you use high quality probiotics(no dextrose,artificial ingredients,biproducts including digest,etc)mixed with plain pureed pumpkin for digestive support.