I don't mean just removing the thumb paddles, but replacing the whole sear block with a non-safety sear block. I thought this was routine, but Apex Tactical told me you can't do it. Is that right?

yes

That link includes the MidwayUSA link for the replacement sear block I bought. But I'm still looking to hear from someone who has actually done it rather than just talk about it.

Then google it. You'll find more threads on that forum of people who have. That was one of the first results. 

Thanks, but I've been googling it all week and can't get a clear answer. I guess I'll be the first person in the world to do it.

I am sure you tried but  Youtube has a couple videos.

Yes, it's completely possible. I've swapped mine back and forth several times on a compact 9/40, FS 9/40, and a 45c frame.

Biggest PITA was waiting for in-stock notifications for the frame inserts if/when you remove the safety lever.

Left side of frame
Right side of frame

Fantastic! So, before you had the inserts did everything work fine, except the ejector was loose? S&W is supposed to be sending me the frame plug inserts, but right now the rear of the ejector is unsupported, and it wiggles. I've been hoping someone can verify that the plugs will hold the ejector in place (and probably keep the sear retainer pin from slipping out the other side). Also I wanted to ask if you had to file the plug a bit on the ejector (left) side to accommodate the new housing?

I'm really frustrated with people telling me this can't be done. Apex surely knows better. I am dissapoint.

I called S&W customer service on Friday of last week for the frame plugs.  They arrived on Friday of this week and I installed them.  It was pretty simple and now the gun looks just like one that came from the factory without the safety.  It also functions exactly like a no-safety gun, the frame plugs do prevent the wobble.  No modifications to the plugs were necessary.

Thanks for letting me know. Hopefully this thread will help others if they search for it too.

I really can't believe Apex Tactical didn't know you could convert the sear. I'd heard such great things about their tech support but all I got was a canned response from their FAQ, despite the fact that I sent them a picture of my new sear housing block with the RAM already installed.

So Apex replied today and says the frame cutouts are different and that the SHB will wobble and make the gun unreliable or ruin the lower/frame. That SHB roll pin is tighter than a tick's butthole though, so I really don't see that being a problem.

Has anyone ever had a problem because of this? The old sear that I have uses the small sear plunger, which I read is known to cause some reliability issues, which is why they switched to the bigger sear plunger, so I don't think this would be any worse than that.

I bought a 2.0 and emailed S&W asking to buy the frame plugs. They sent them to me free of charge.

Did it with my 45 version years ago.

i pulled the safeties off my 45 version years ago. i dont believe i did anything except put the frame plugs in and move on.

I believe the 45acp was built to easily convert between safety and no safety sear housing blocks. As is the 2.0 I think, and possibly some of the later model M&P9/40's. But my M&P9C is the original design, the one with the 1/16" sear plunger.

So as it turns out, the plugs--at least the ones they sent--are not compatible with the non safety SHB. I was able to trim them down with some wire cutters and a file and make them work. The ejector is now sturdy. The right side has a gap that appears to allow the sear retaining pin to slide out pretty far, so that's the only think I'll have to watch out for.

Not only did I have to trim the frame plugs, but I had to squeeze them in on top of the SHB, and so I put a dab of super glue one the right side so it doesn't fall out (it doesn't serve any purpose other than aesthetic, unlike the left side, which holds the ejector in). I wouldn't recommend anyone try this who isn't fairly confident in their abilities to work on guns, but I am happy with the results because at least I can use the Apex RAM now.

If I ever sell the gun I'll put the original SHB back in it. Right now it is a range gun, but if I can get 200 rounds down range without any issues then I will use it as a nightstand gun.

I'm guessing the OP has one of the original M&P's.  They use a different sear block etc.  If it takes a ram it is an older one.

 I think you used to able to lock them as well.

They have a round hole on the left side with an arrow.

I do not know if the later sear block are interchangeable in those frames.

I take it that you can't just remove the safety paddles and spring?

Yes, I could've done that. But my trigger reset that was terrible to begin with had gone away completely. That and I lost the tiny plunger under the sear, and S&W doesn't even have those available anymore. I wanted to improve the trigger, and I had to replace the entire sear block anyways, so I ordered a sear block with the hole in the left side that would accept the Apex RAM.

Long story short is that it worked. The RAM significantly improved the reset, and everything fits, although it did not fit perfectly. I did not have to alter the frame or the SHB; I just had to trim some plastic off of the frame plugs. The left frame plug is what holds the ejector in place, but I had to trim it because it was catching on the rim of that hole he RAM goes into.

Total paid for the upgrade was $25 for a new SHB at MidwayUSA, $11 for a new ejector (because that's the only part the SHB didn't come with), and $26 for the Apex RAM (not required, but why not?). The frame plugs were sent free of charge from S&W tech support.

Here it is after completion: