Zesty

conversion factors are set by the exchange for each bond and delivery month......as time goes by the level of underlying rates/curve may change.
As the group of deliverable bonds will be of various maturities and coupons the ctd may well change over time...This is often the case....more often down to repo conditions, I have found.

I didn't pay much attention to this section, having traded quite a bit of basis in the real world.

I have used;

basis = cash/spot price of bond - (futures price x conversion factor for individual bond)

This has been known to make money on occasions!