Fair enough. I've done it three different ways:
1) bag drops with clean clothes at 350km-ish intervals on LEL that didn't necessarily coincide with my sleep stops
2) carrying everything in a monster saddlebag for a 1300km DIY
3) not changing shorts at all on PBP
It doesn't really matter - clean shorts are clean shorts - they'll be just as welcome at lunchtime as first thing in the morning.