Clearances are set by the netclass in KiCad, but I often need a different clearance at specific locations of the same net. Particularly when fanning out from a tight pitch BGA or QFN part, and sometimes when layout out power traces. I have heard that RF layouts need to do this also.
The only way you can do this right now is a bit of a hack. You can change the netclass clearance as you do your layout. DRC is no longer valid for nets that you do this to.
I have written a patch to KiCad that lets us set the clearance on the fly if needed. https://youtu.be/05vfAvYwDio
I’m posting here to see how many others besides myself would find this to be useful.