Not a cut off, but I added a Bidet. The connector that came with the Bidet would not seal on the toilet where the pipe connects. After a couple trial and errors, I finally realized I had to cut the PEX line to do it right. Got the T connector from my RV dealership parts department and the bathroom toilet valve from Lowes.
No crimping of the PEX involved. Very, very easy to do and no leaks in over a year now of traveling and using at home.
It would be very easy to install a cut off valve from the T to the toilet, in addition to sprayer, or in my case, the Bidet.
Here's one I added to the line going to the refrigerator ice maker. I wanted something rigged up a bit easier so when I winterize and unwinterize, I could purge the water or the pink-stuff from the line, much closer to the refrigerator. Before I added this, I'd disconnect the line right here. That got old, real fast.