Adding weight to a VEXIQ robot is never a good idea.
Can you describe your robot? Maybe a picture?
Until you do that, let’s take Clutch as an example.
When you load a Cube onto Clutch, it has a tendency to lean forward, almost tipping down. Now one solution would be to add weight on the back to help counter the force.
Plan B would be to extend the chassis to move the front wheels 2-3". This longer wheelbase gives you better balance, it’s moving the center of gravity. Two 8x2 plates weigh almost nothing.
Good luck!