Only modification possible is to cut the band and use it as a long strip or as friction material.
You cannot use the rubber bands as an energy storage mechanism; i.e. a triggered projectile launcher that releases energy from the rubber bands is prohibited by the rules.
You can use the rubber bands as a friction material, as a static tensioning element or as a dynamic tension element, for example, an idler pulley that keeps a power transmission belt taut. Energy can be stored in the rubber bands; it just cannot be released.
Rubber bands can also be used to make flexible plastic hinges.
When applying the bands to wheels for added traction, you should not apply them axially across the wheel. You should place them in a chevron or diagonal pattern to minimize shear force on any one band and improve the smoothness of the rolling action.
To modify you can use the following tools: X-acto knife
You should not use: Mill, Lathe, Shear, Notcher, Punch, or any other power tool.