how could i mod the LAAT's odf so that i could increase the maximum ammount of units it could hold?

I don't think you can, you would need to edit the model in XSI and add hardpoints.

You could add a couple of extra passenger slots. I managed to get two troopers standing in the troop compartment at once through ODF editing, but the camera was kind of wacky. (I probably could have fixed this had I taken the time) Also, you can add additional passenger slots and simply not have your unit show up in the gunship's troop bay.

EDIT: Here's a pic. It's actually not that hard to do, you just need to experiment a bit with the ODF.

Are there hard points there in the model? Or did you work some sort of ODF magic?

I think that they are built into the model.
Think back to the Utapau campaign video.
It shows two clone troopers hanging onto the bar just like in the screenshot.