ambient temp deice fluid is OK, just SLOWER
Major carriers like it hot because it works so much faster--instant gratification! But the chemistry is the same, whatever, so if you've only got it cold, go ahead and use it. (If the deice fluid itself is solid, take the day off!)
Rotor head deicing? Hmmm, a judgement thing--the aerodynamic penalties for icy swash plate are minimal, so if the linkages are free maybe you could just do the blades.
Used to be a mountaintop weather observer (Mt. Washington, New Hampshire, 6288'), rime feathers built upwind on all our towers during storms (in cloud), once they got 3 or 4 feet long (50-100 pounds typical) we roped up the tower with an 18-pound crowbar & beat the bejesus out of the tower to knock off the ice. Which disappeared horizontally into the fog downwindward. Not, however, a suitable method for your rotor blades.
One of our guys was in a hurry, bashed a feather above his head. He was only 20' up, but underneath it when it hit the ground. Got out of hospital in just four days with multiple broken ribs. Almost, but not quite, received a Darwin Award.