I talked to the guy in the Microsoft Store last night - they are good with any sort of return within 30 days.
My thinking is that I have a couple of weeks to see if the upgrade is worth the money (coming from a Rift) and while I love it now, it’ll be interesting if I love it in a week or two. It’s better, but is it $500 better? 
Will do, just got to get through the DCS update for today, reapply the VR mod (that’s pretty much vital for 30-40% more FPS in VR btw @chipwich and @BeachAV8R and so worth it) and then I’ll Viggen it!