I went ahead and took the nipple off and decided I'd use it further downstream at the bottom of the tee I had to put in as a moisture trap. I simply replaced it with the coincidentally identical nipple I'd bought at the store.
Here is a shot of the instructions on the joint compound. Honestly, I took a picture of the instructions so I could look at the back of the camera and zoom in and read them.
I had to remove the bracket holding the CSST/tee/CSST section to the bottom of the joists so I could turn the nipple into the tee.