If an aircraft which normally falls in the Approach Category C (Speed 12-140) has an approach speed of more than 141 on a particular approach due to some reason like a failure which necessitates a higher approach speed or due to the aircraft being heavy, will the DA also change?
The category that applies will be based on the higher speed. If you fly a cat c aircraft at a cat d Vref you must use cat d minima. However you cannot do it the other way round and reduce the category the aircraft was certified in. Of course, in an emergency you will do whatever has to be done.