OP's approach looks cool but a bit baroque. I'm also hacking around EDID issues and it turns out there's a nice GUI program to decode and (lightly) patch it: https://packages.debian.org/unstable/utils/wxedid

I have to do more involved full EDID reconstruction surgery tho since I need to add DTD entries rather than just change existing ones. So I'm looking at [edid-generator] together with [cvt12]. The latter can calculate xrandr modelines for VESA standard timings that all seem to work with my TV. cvt12 adds the option to calculate NTSC (1/1.001) timings over regular cvt which is already in Debian.

[cvt12]: https://github.com/kevinlekiller/cvt_modeline_calculator_12

[edid-generator]: https://github.com/akatrevorjay/edid-generator (thanks Kodi wiki)