Always lots of chatter about this and options. I chose to modify my OEM CCT and will continue to use it with the top-end rebuild.
I added the "bolt" many years ago and at that time the "plastic" sprocket was worn down to about 1/2 it's diameter. The "roller" was good !
Adding a threaded insert keeps the Shaft from retracting fully; not allowing the small 10mm bolt to hold the shaft in the retracted position. Not a big deal: Just used a slightly longer 10mm bolt and when installed the longer bolt is removed and the short original reinstalled.
However: Now with full diameter roller and sprocket (plus the insert); the shaft may not retract enough to allow the CCT to be installed. The full diameter of the roller and sprocket effectively shorten the chain relative to the CCT. The CCT will be more vertical - The shaft must retract more. The "spacer" if required, will deal with this. The "Thumb-nut" on the back-up bolt was very deliberate. "Finger" adjusting !!!! If you choose to use a wrench to adjust (tighten) your CCT tension; Your going to quickly and eventually "F" up your plastic and rubber "spinning" parts !
Hope these makes sense.