You said easy, but fooling around with a safety gives me the heebie jeebies. An Ed Lapour replacement isn't "easy" but would be another approach. That's pushing 300 bucks these days. Do you have another rifle that doesn't snap? 2 cents
Well whether it gives you the heebie jeebies, it really is a very simple affair. Safeties in general tend to be a very simple device, and a quick look and it will seem intuitive because of its simplicity. If I were taking the job, it would be about $50.00 and that mostly due to the time spent unpacking, packing, and disassembly which is twice the time spent on the actual safety itself.
The thing with doing work on a safety is you want to make the change, check, file a little, check, file a little, check. It's never a one and done sort of thing, but something you take your time on and go slow. But it's really quite easy (for most guns - again, I'm not familiar with the safety on the ZKK)