James, I’m assuming you have a abs2 with lbs/tcs/abs?
Since you said YSS springs is -2cm shorter, is the bike front end sitting lower now?
If YSS does not specified changing spacers/collars length, then I suspect front preload might change lower, when I replaced my springs from factory to progressive suspension, aftermarket springs was longer hence PS recommended to cut a spacer ~83mm to replace original longer spacer in non cartridge side leg.
You probably could do this fine tuning later on without removing the forks from bike later on if you find the front end sitting lower.
Hopefully the oil height specified by Yss is correct as well, as I think most of us goes by the factory height/oil setting measurements with springs out. Enjoy your ride!