oversized factory pipe screws

i have a factory pipe that came on a 750 sx i bought and the adjustment screws are seized and broken does anyone know if they make oversized screws if i get it drilled and tapped or if there is anyway to getting them out the right way i guess the overall goal im trying to achieve is to get new screws in that i can adjust
 
i have the old old factory pipe which only has two tuning screws on the outside and a small hole on he inside that can ether be open or closed. i was told closed is for bottom end and open is for top end now if i was able to get the first screw drilled out would i be able to weld over the screw hole so that it is permanently open if anyone is catching my drift
 
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