How do I assign custom name to each GPU in the rig? I did that a while ago with one of my rigs but totally forgot how to do it, search didn't return any answers. I want to be able to later assign clocking profiles to them based on names (which include manufacturer/model/cooling type)
There are unfortunately no great feature for this today. For a selected miner, on the GPU tab, you do have a button for "Set name", but it's a bit limited at the moment. The name will only be used on the GPU tab itself. A future improvement would be to display it everywhere if defined.
Interesting, I think I saw it somewhere in the manual, OC settings rule based on GPU name?
You can define Clocking Profile Groups (see the Options dialog, GPU Clocking Profiles, where you find the groups as well) looking at the reported GPU Name. This is however the true name of the GPU like "nVidia GeForce RTX 3090", not any custom name you defined yourself.
With the Clocking Profile Groups you can for example define that all GPU names containing "3090" should have one profile or all GPU brands matching "ASUS" should have another profile and so on.