I could keep my nice kickflash contents, and boot MOS whenever I wanted via early start-up menu... now with OS4 I had to erase completelly kickflash.
I don't know with kickflash, but with Algor/Romulus it boots normally. If you want to use Norway you simply disable flashrom contents using left mouse button and you are done.
Just change your OS4 kicklayout file so you set booting device to be OS4: (or whatever name you choosed). You have to create a small text file.
That way your system will boot normally OS3.9, and if you choose MOS or OS4 in the early boot menu it will boot OS4 or MOS. I don't see the problem.