The stock lower steering shaft has two plastic "pins" in it to determine length. They are not meant to remove to allow telescoping. Even drilling them out will not allow you to make the shaft safely longer. They are made of plastic so, in case of a head-on collision, and our chest hits the steering wheel, the column will collapse. That's why the upper column is held in only with clamps. Some aftermarket shafts are made the same way, but with easily shearable rivets instead of plastic pins.

On the other hand, some quality shaft upgrades, like Borgeson, are made to telescope up and down prior to installation, for a fit on vehicles that have a body lift.