I built a similar thing, primarily for my own fun. As a reaction to various C64 tools being scattered/old/unsupported exes and often with not OSX builds, my approach was to build a low-friction web app, which I could mess around with easily across whatever machine I was sitting in front of, whenever I had a few moments (kids...)
Examples : https://46c.io/project/NVXAZ7JY/code/ram/0E2B https://46c.io/project/8VM2EY7T/library
Basically : select a byte (or a range with shift) and use the buttons at the top to tag it with some metadata like a label, a comment, mark it as the lo/hi byte of a pointer etc - and it'll update the disassembly immediately. It saves all your work in browser local storage by default but if you sign in you can work from 'the cloud' (cheapo Firebase account) - I haven't shared widely before so no idea how that will hold up to the HN effect...
Enjoy!