Southwest Rapid Rewards - Business Select & flight change

So I have got my BS tickets and my inbound International flight arrives a little earlier than I expected, early enough to take an earlier WN flight. Now I know that if you have hand baggage only you can go to the gate or desks in departures (I think) but what if you have luggage to check in can the check in agent change your flight & tag your bags for the earlier flight (assuming there is space).
Also what boarding group would you be in would the BS A1-15 be valid or would you just get the next available No.
Thanks

Yes, the agent checking the bags can change your flight and give you a new boarding pass. Whether you would get A1-15 depends on how early before the flight you checked in and whether any BS positions were still available.