So I think the answer you may be looking for is this. Glocks use a 5/16" lag bolt or a 5/16" carriage bolt, easily picked up at Lowes or Home Depot. I have replaced several this way. I understand this is an M&P question, not Glock, but the methodology is the same.
You insert the bolt down into the channel and up against the liner. Partially then the bolt so the threads bite into the old channel liner, and pull it out.
Slide the new one in, and push it all the way in with the striker. I have done with several Glocks this way, it works. Just need to verify the size needed for M&P...
I found it on Youtube ....
Also, a bit of knowledge, the MGW Glock sight tool fits M&Ps for the rear sights as well, comes in handy when doing Apex triggers and the only tool available is a Glock sight tool, fits great. If MGW fits, the OEM Glock tool will as well.