For supermotard, the front of the bike is lowered to minimize wheelies
The suspension travel is shortened, about 4 cm or 1.5 inch, but without having to cut the springs, so you can always change it back.
You can also slide the fork against the handlebar if you like(that's about 3cm, i guess), it's less work than the job above when you want to switch to offroad trim. But the first way is better, because of the preload on the spring.
For monobike, both the front and the back are lowered.
But when you change the front wheel, it also means changing the brake. And when you use a 4 or 6 piston caliper and a stronger master cylinder, the entire brake system needs changing.
Also, when you change the back wheel, note that the difference between a 38 and a 49 teeth sprocket requires the chain to be shortened/lengthened.
You can also make a complete setup using a second fork, with the front wheel already in it and the brake system installed and replace the front as a whole.
Then you just need replace the master cylinder on the handlebar and you're done.
I will post more pictures in my gallery soon, but in the meantime:
http://www.kxriders.com/coppermine/index.php?cat=10893