What happens to k once d hits zero?

Am I correct in thinking that even after d hits 0 that changes to k will still be possible? And if so, will those changes to k be made/approved via Voltaire voting?

Changes to K can be made at any time unrelated to the D, or other parameters so yes. Obviously other parameters need to be taken into consideration.
After D = 0, Voltaire voting, yes. (Possibly even before that after d < 0.5