first start break in

I once had a brandy new stat stick closed during the break in procedure. Thats why I always use the restrictor washer.Theres nothing like a good panic to make you rethink your methods.
And I always use water during the cam break-in, and often for the first couple of hundred miles. It is a far superior coolant to anything else. Once the engine has a reasonable tune in it, and shows a history of not running hot, then the 50/50 can go in. I would hate to lose an expensive engine to something so preventable.My bosses always have liked that about me, when I dont cost them money, needlessly.

Oh yeah, drill the stat for sure; theres no down side to that.
And yes you can refill the block through the stat house, if you like.