Ferrite Cores for EMC Solutions

I have found I need to insert a ferrite core around a cable in order for the equipment to pass EMC suspectability at 100V/M.
My question is the core is specfied down to -20C . The spec of the equipment is -40C.
What detrmental effect if any will this temerature have on the ferrite core?

You'll review material specification for the respective ferrite type, or refer to general data in text books. Most ferrites have linear (decreasing) permeability over temperature between +50 and -50 degree C, some have almost constant permeability. If you passed the EMC test with some margin, there should be no problem.