I have a blue 09' that came with the factory side cases and I did it with just a small amount of tweaking. I used a Givi FZ447 Top Rack Plate and a Givi 52 Maxia top case. I really like the set up but I had to tweak the bars that extend out towards the back of the bike just a little bit.
The problem is when you bolt the 2 pieces onto the area that holds the grab bars it's a really tight fit, but it can be done. When you do this the bars are then pointed a little bit too far in towards the center of the bike at the back end. This causes the top mounting plate holes not to line up with the bars mounting holes. All you need to do at this point is spread the bars outward a little bit.
I bolted them onto the bike and stuck a 12" screwdriver into the length of the bar (had to take the rubber/plastic plug out of the end). I held pressure outwards with the screwdriver and whacked the bar with a heavy rubber mallet. I hit it right about where the bar just starts to turn downwards and a little bit on the straight portion both places at the same time. I gave it 2 pretty good smacks and did the other bar. The bolt holes on the top plastic part (the top mount) that the top case bolts onto only liked about 3/16" lining up at this point. I gave each side one really small whack (with the same procedure as above) and it fit perfectly.
The whole process probably took me 5 min. longer than a straight forward install would have. Everyone told me it wouldn't work but I had a friend with the same toprack and I kept looking at it and measuring it. I decided it could work with a little tweaking. Glad I tried it as it didn't take as much rework as I thought it would and I am extremely happy with it, aaannd I can lock stuff up or take the case into the room if I want to.
I picked the Maxia case partly because there is an electrical connection (for lights) that goes onto the top mount that works without a connector that has to be attached to the top case. In other words you just place the top case on the mount and the electrical connection works with no wire hook up or connector between the top case and the mount.
Some of the other Givi cases may do the same thing, I'm not sure. I also like the amount of room in the Maxia. I cannot tell any difference in the handling of the bike with this size top case. However I am not a rider who pushes it to the extreme (just some times
If a Givi top case is what you want, I'd say go for it unless you're just not comfortable with modifying things a little. It really wasn't that hard to do though.
Good luck which ever way you decide to go, JH