Just wrote a little blog and made a video about this to hopefully make it easier for folks to figure this out. I’ve looked it up a few times throughout the years and it was always a little tricky to find.
https://blog.rayberger.org/how-to-add-a-brand-preset-to-openstreetmap
In case someone has a JOSM preset and wants to merge it into the NSI, here’s a (very hacky) script to do that: https://github.com/balsoft/josm-ge-preset/blob/70033d097a72f54602b903878b2a89228bbc5dbb/toNSI.py
You’ll definitely want to change the
commonEntryKeys = { "locationSet": {"include": ["ge"]} }to your country, and maybe some other things too.Thanks for sharing your script. I added a link to your comment at the end of the post 👍 I gotta learn JSOM one day.