So I'm all for preventative maintenance. However, when it comes anything related to the A/C system, I would rather let the pros deal with that. I am advising you to avoid releasing the coolant fluid in lieu of replacing the evaporator. Those things don't really tend to wear down anyway unless it is exposed to atmosphere for prolonged periods of time.

Have you had any problems with leaks in the A/C system? If so, replace the evaporator and all seals on the hard lines. If not, don't worry about changing it out.

89 Raider - V6, Automatic, rear LSD, A/C Retrofit, Cruise Control Retrofit.