On some reflection, I agree with <PERSON> that immunity in a biological context probably isn't possible for cyanide, but, with some heavy modifications, it should be possible to engineer an organism that is resistant to all levels of cyanide it is likely to encounter. You're not going to achieve this with just a single modification, but a number working in concert should get there.
Modification of Cytochrome oxidase C would be possible - there's probably an enzyme alteration that would prevent cyanide from binding to the iron ion in the enzyme. This would be hard, though. Cyanide is a very strong binder of Fe+3 ions, and this is likely to be hard to defend against. This paper suggests that swapping in an alternative version of cytochrome C into the pathway confers good resistance, and is well tolerated in mammalian cells. 225
(https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1456879/)
An easier method is to do what, classically, the body does with toxic compounds, which is to have specialist enzymes to break down or manage them - In cyanide's case, it might be as simple as having a lot of molecules with Fe+3 ions to mop up the cyanide - a modification of hemoglobin would do this, and, in fact, one of the antidotes creates a modified form of hemoglobin (but causes a drop in oxygen transport in the process, because it uses existing hemoglobin). An enzyme would probably be involved in recycling the modified hemoglobin. Thiosulfate cyanide transsulfurase might work without modification, to convert the cyanide into a much less toxic substance, which can then be excreted.
Finally, although I've not found an example for cyanide with a quick search, the other, classic, method for control of toxic substances is to remove them from the location in which they'll be harmful - I can't find something like a cyanide pump, but this would be another, biologically plausible mechanism to add resistance
The modifications would be pretty energetically expensive, though, and are unlikely to evolve in a normal environment. Your proposed organism would have to be full of modified hemoglobin, requiring a large amount more iron. Getting this would probably require an increase in food, particularly red meat (being a good source of bioavailable iron) 938