Is it possible to use a control scheme with a delay as prefilter?
1 - It can be a good idea to put a filter $C_r(s)$ in order to smooth the reference. For example, if you have a speed regulator, and the reference jumps from 100 km/h to 200 km/h, having a low-pass filter will smooth the actual reference fed to the closed-loop. It could prevent excitation of unmodeled dynamics, actuator wind-up, etc. That being said if $C_r(s)$ is a simple delay, it has no purposes as far as I can see.

2 - $C_r(s)$ only affects the reference fed to the closed-loop. It will not affect stability of the closed-loop like you mentioned. It also has no effect on disturbance rejection or errors due to modelization (such as unmodeled dynamics).