I created the same mod for my MMR. You can purchase acrylic spheres from US Plastic corp. They are located in Lima Ohio but also have a wesite. I used a 3/4 inch sphere and it worked great.

I installed a set of gold mirror blades from PDI and they look fantastic. Since there can be variation between games, it is best if you measure the total available side gap. I believe I measured 3-4mm. No issue with lifting the playfield with them installed, just go slow.

I own a MMR LE, added color to the display, and am considering the new XL display.
Q: What is the anticipated resale value of the old display/grill assembly? I assume the color chip stays with the XL.

I had the same issue with the swords shooting off the flippers during game play. The original adhesive didn't work nor did CA. Ultimately I found 3M adhesive transfer tape with 300LSE ( type of adhesive). I don't recall where I bought it, but it is professional grade stuff. Works great and the swords have not come off since. Transfer tape is very tricky to use, so you will need to place the sword on the sticky side of the tape and trace around it using a new xacto blade. Be sure to remove the old adhesive first.
Clean the flipper surface with alcohol and apply.

By the way, 300LSE was selected because it "provides high bond strength to most surfaces, including low surface energy plastics such as polypropylene.....also provides excellent adhesion to surfaces contaminated lightly with oil typically with machines parts".
It only came in a roll but I have found uses for it since.
Good stuff with CA doesn't work.

The 9474 option interests me because it claims it is easier to cut than the single layer version (this version was not available when I purchased).
It also claims high shear strength, which is what's required with a metal sword on a flipper bat.
Given that both options are cheap, I would get both in the event the 9474 doesn't work.
Good luck, I will be interested in hearing how this turns out.

Would this connection (from post 7545) work with other speaker and flipper button RGB LED sets? Normally these are connected to 12v.

Thanks for the feedback and for providing the insight into doing this. I already have a topper with its own power supply, so only the speaker lights were added to the circuit. Works great so far. What problems would I see if the circuit was unable to handle the load?

I used a small piece of Mylar to ramp between the steel lip of the protector and the playfield. Can't see it and never had a problem since.