I saw that EaglesBlood released a pre-alpha of Jelly Bean for the P999. Is it possible to make this boot on the O2X P990? I live in Europe.
You may be able to boot, but the likely hood that things like the camera, wifi and other things, working are slim. Even when it is "the same device", just a variant (like the vibrant, captivate, galaxy s, fascinate, for example) flashing a ROM not made for the specific device will not work.
The differences in the hardware causes modifications to the ROM. Everything from the wifi chip, to the camera can require custom drivers.
Most likely, you wont even be able to boot though.