Tillamook,
It can be done, in fact it is standard in the control system I have designed where my Vent set point is dynamic based on DB temperature and evaporation rate
Standard schedules, be it time or MC% based works on the assumption that you can achieve and run at set point - so when steam supply runs low - so will your DB temperature. The vent set point stays constant and your vents stays closed for this time. The ideal is to reduce the vent set point when "energy in" is reduced...to keep on removing moisture, although at a slower rate. The opposite when steam pressure is restored again...vent set point must be increased.