So this is how it works:
For the military match it happens it December. Every HPSP student HAS to go into this match, everyone. Depending on the specialty you are applying for, you will have a military residency, civilian deferred, civilian sponsored, or a TY year. The Air Force has a lot more civilian deferred/sponsored residencies- so if you want a civilian program your odds are better with Air Force. To my knowledge the Army only has civilian spots for surgical specialties/subspecialties- and those are civilian sponsored (more on what that means later) I know nothing about the Navy and their match.
It's also more dependent on specialty. For IM/FM/Peds there are very few civilian spots, and even in those specialties they dont fill their military match (that has to fill first before they will spill over to civilian spots). The subspecialties have a lot more civilian spots.
The difference between them all is the military residency pays you as a captain, you make significantly more than residents. Weakness are usually acuity of patients and patient load, these residents are usually academically very strong but their clinical reasoning appears weak. Civ defferred you are approved or THAT SPECIALTY ONLY. If you are civ defferred for emergency- you cannot apply to 9 ER programs and then one IM as a safety...you'd get in a ****load of trouble if you somehow matched into your IM safety. You make what a resident makes (but no sudent loan debt), but generally your training is better. After residency you go back to the military to pay back your 3 or 4 years. Civ sponsored you match in to a civilian program for THAT SPECIALTY ONLY, and the military pays you as if you were in a military residency. You make that sweet, sweet money- but the bummer is that for every year the military pays you as a captain for that residency- you owe them another year of payback (so for a 3 year emergency residency plus the 4 years for medical school thats a total of 7 years of payback).
For the match you will list your order of preference. Most peoples list goes: 1. Military residency, 2. Civ defferred, 3. Civ sponsored. You also have to make a list of TY's that you would be willing to do if you don't match into any of those options.
So, to answer your question: your scenario you propose if you are accepted to and accept the HPSP scholarship is literally impossible.
Choose carefully, this is an important decision.