Presumably, This hypothetical windsurfing North Korea, that imposes this absurd scenario would force companies to build gear that covers a larger wind range..
So I would have my tear away 5.3 S-1 that turns into a 4.5 and I'd build a custom board with replaceable rails, maybe an adjustable rockerline which turns into either a 78 wave or 100 freestyle..
The adjustable board is a workable idea under current laws, I sailed an evo 71 over summer and the only difference between that and my freestyle was wider rails (freestyle has sharper rails also).. fins, footstraps, rocker was all the same...
* I think there is something in this, it wouldn't ad any weight, and would be a lot cheaper than buying two boards. It could also work for a little wave into a big wave, or slalom, anything really..