Yes it is possible using the VboxManage utility.
It has been at least a couple of years since I did this, so be sure to
check the current documentation in case it has changed!
Code:
VBoxManage modifyhd FULL_PATH_TO.vdi --resize SIZE_MB
This changes the "drive" size but NOT existing partition sizes! You must then resize partitions just as you would a physical drive. Booting the VM to a Gparted live iso can do this without data loss.
Does NOT support downsizing.
Does NOT resize snapshots.
