Random early morning thoughts.

Would it be reasonable to chamfer the slide stop hole in a 1911 by hand? Make it a recess slide stop pin as seen on some custom 1911 or HRT spec guns?

Maybe by using a pilot reamer like for increased the lead on a barrel?

I’m willing to risk it if so.

Interesting. Seems like you could recess the pin without chamfering the frame. Function over form.

Typically, countersinking is done when the cutter and the workpiece are rigidly positioned.
Pistol frame securely clamped into a fixture, countersink tool/angled carbide insert cutter in a collet/toolholder mounted in the quill of a manual or CNC milling machine.
I've never seen a machine shop style countersinking cutter with a pilot, but it certainly would be possible to get one made at somewhat considerable expense.
It is possible one is already made specifically for the 1911 chamfered slide stop pin hole and doing it by hand. (perhaps contact Brownell's?)
They do make them for gunsmith style hand work specifically cutting custom angles/cleaning up gun barrel muzzle crowns.
With "freehand" countersinking, (without a pilot and/or rigidity) quite frequently "chattering" takes place, leaving behind on the machined countersink angled surface, cutter chattering marks.
Once chattering takes place, the only cure is to go deeper which has another set of concerns/problems in a firearm. You don't want to end up with a chamfer the size of a dime.
It will be far cheaper to farm the job out vs having a piloted hand operated cutter manufactured if one isn't readily available on the commercial/gunsmith tools market.
Just pay somebody qualified to do it for you.

Thank you. This does indeed seem more than I can manage.

I will probably trim the slide stop pin just a tad and see if I can put some serrations on it.

No particular reason for any of it for me but not something I want to ship the gun off for.