Question about Key Generation and Builds

We have a Build that has passed submission. We are about to submit a new one but would like to generate some keys. 

Can we specify which build the keys will download or will this always give the user the latest submitted build to get approval? 
If the keys are build specific are these no longer valid when the new version is approved? 

Also if a game is on applab but moving to the store, would the game need to be moved over before you are able to generate the keys?