To see if there are any leaks in the exhaust , you can close off the exhaust with your hands ( or a cloth if it's to hot ) while the engine is turning .
If there is a leak you will hear it . Normally you should be able to shut down the engine this way before the pressure forces your exhaust to...
If you don't make the hole to big I don't think you can harm the bike .
Still you are at your own risk , and only do this when the bike is used on a racetrack ;)
Yes the bike still runs smoothly , you just get a little more deep sound , more like a motorbike instead of a sewing machine .
I think drilling is not going to work because of the bend in the pipe .
And on the " how did you know " question : had good results in the past with an SV and after...
https://www.youtube.com/watch?v=pJFoYIv0kNE&feature=youtu.be
I used a 1 cm thick steel rod , with a point like a screwdriver , stuck it in the rear of the exhaust and used a hammer to drive it through the side of the endpipe .