IIRC, that pin is a "roll" pin. They can be removed from a 'blind' hole, it just takes some doing.
There are collet type devices which compress the pin lengthwise so that they can be started (and in some models completely inserted) into the hole more easily. In those models they cover the entire length of the pin. If enough of a stub has been left it's just a matter of working the pin free by twisting it back and forth while pulling it towards you.
The main problem with trying to do this with another type of grasping tool like pliers is that most of the force exerted on the pin is concentrated on too small an area, and in the wrong way.
The result is not getting enough compression laterally, along the axis of the pin, to release the part that's in the hole so it can be pulled out. And usually winds up crushing the pin at the point of compression and twisting it in two trying to force it out.
If you choose to grind, file or cut off some of the pin in order to remove the latch, leave as much of a stub as possible. you might be able to use a roll pin starter tool and some penetrating oil to remove it completely.
Then you can just get a new roll pin of the proper diameter to install and trim to fit.
Another option, IMO, is to just keep the retaining bolt arrangement (or a spare) from your Tech sight or B-Square-type scope mount and use it.