You can change the default store of one or multiple products very quickly using Store Commander's multistore options.
Once you have selected the product(s) you need to make the change onto, open up the Multistore Sharing Manager panel from the Properties column.
All you need to do now is select the targeted default store by clicking on the corresponding radio button
This is it! All selected products are now using the shop 'Store Commander' as their default store in a few clicks only! Fast and efficient!