1. Can players opt to not use their role's powers? For instance, if a player is [...] playing the Medic, can they "turn off" the passive cure and spend actions to treat (and therefore place cubes in the lab)?
2. In a similar vein, can the Quarantine Specialist opt to "turn off" her quarantine ability and allow disease cubes to be placed anyway?
3. If a cure for a disease is discovered, do players have to treat all of the cubes with one action?
can players disregard role powers when they are detrimental
This is not something unique to the Lab challenge. For example, in the regular game players sometimes want to turn off the CS, QS, or Medic abilities to preserve disease cubes for the Field Operative or to enable better use of the event Rapid Vaccine Treatment.
Matt and I made the decision to not allow this to avoid adding lots of extra decisions and rules overhead.