Hello Catra.
Having had RSD since '83, I won't go to any extreme.
Including Ice.
I also suffer from migraine / cluster headaches.
Sometimes,
Cool is cool.... if you understand. It's Up to you!
Ice, I say No.
But, cool, sometimes you may like. (And, this is an individual preference).

I've had my feet swell. And, for swelling, Heat does NO Good! Right? Of course, we all know that!
So, I take these Hydrocollator packs (from a Chiropractor, or medical store), and I keep them in the freezer. I would NEVER put them directly on my skin. But, and however, if, and depending, I'd wrap them in a towel, and put them over the instep of my feets.

And, still, towel wrapped, on my forehead, or anywhere it feels good on my head, even neck, when I'm down with a migraine!

I don't like the ice packs directly on my skin.
But, don't let anyone tell you a "law", you cannot do this, or that.

For Migraines, the cooling effect is just what the Doc ordered, because of the constriction/dilation of the blood vessels. The "Cool" is wonderful~!
Same on my feets.

So, you may like it on your knees.

For me, the key is,
"Cool, Not Cold".

There is no law, no absolute in my eyes, or my world of pain.
It's whatever works!

Also, the Electronic Stim, or, "TENS" unit, works wonderfully as an adjunct, with heat, or cool.
I say cool, NOT cold!
Cool helps reduce swelling. Heat? Works the opposite. So, take it from there, and use your feelings and intelligence.
You'll find a way to make it feel better!

pete
asb