You are not just drilling the Block. You are putting a hole in the Rib as well!
On the restorations I have had recently, many of the Basses needed a new Block and these only had one hole in it. Out of 8 Basses opened up, 4 or 5 needed a new Block (I don't recall if the Gilkes was replaced or trimmed as it
looks old but
not as old as the neck block).
I can't imagine how a Block will last with two holes being drilled. I have only seen a few Basses with a separate Tailwire Socket and separate Endpin so I can't say for sure if this weakens the Block over time but using either Endpin over time is double duty on the Block itself.