The heating of honey should always be done carefully and slowly.
For example; With honey in a 30lb bucket I would heat at 35C to liquefy the honey for bottling, provided the heating cabinet does not have any 'hot spots'.
The diastase and HMF factor will not be altered to any great degree.
Honey should be heated for as short a time as possible so the honey will remain unchanged from its original state.
This whole concept of heating honey can become very confusing.