How hard would it be to switch from National Guard to Active duty prior to ship date?

You wont be able to switch prior to voiding your ARNG contract and then enlisting again through AD. Active Duty Army and USAR recruit separately from the ARNG, because unlike AD and USAR, which are both entirely federal entities, ARNG is also a state entity, which is why when you enlist in the ARNG your oath of enlistment includes obeying the orders of the applicable Governor. National Guard recruiters in their respective states are recruiting exclusively to fill unit vacancies within their own state, and that state's National Guard bureau funds the training seats for BCT and AIT.

You can either request to be a Future Soldier loss from the ARNG and then see an AD recruiter, or you can attend BCT/AIT with the ARNG as you're scheduled to, and then submit a DD Form 368 (Conditional Release Form) after a minimum of six months back with your ARNG unit, requesting to go AD. Mind you, there are no guarantees either way. If you decline to ship for the ARNG and decide to enlist AD first, you're not guaranteed to receive the same MOS you enlisted for with the ARNG, and if you go to training first and request a conditional release to go AD later, your state ARNG bureau is not obligated to approve it and let you go. Best of luck to you either way.

It is not as easy as you might think. The National Guard has committed funds toward your training. Your best bet is to immediately ask your recruiter and see if something can be worked out.