Swapping wheels and cassettes with Shimano GRX 600/800
My experience with swapping wheels is disappointing.
I had to adjust the derailleur (limit screws, cable tension) and rim brakes (due to slight difference in rim width and dish) every time I swapped wheels. Maybe if you have exactly the same hub and rims on both wheels it will work better. I think my derailleur adjustments were necessary because the cassette position was ever so slightly different between the two hubs.
The longer chain should work fine on the 11–28 cassette. After all the small-small combination is the same, so your rear derailleur should be able to tension it enough.