How can we form our own customs that protect us from assimilation

1. memeing - this is what most people are doing because this game is natural for our times. See punk6529's twitter treads - he's a self-described meme maximalist and seems to seriously believe that NFTs help in this quest. 3D games / VR are an important vector here. There was a Bitcoin-focused Minecraft server advertised here recently; I think it failed "choosing and rejecting technologies based on their potential to control and surveil you" miserably so I didn't comment on it but others seem to like it.
2. Balajism - read "The Network State". Your dive into Zomia is what Balaji describes as "history mining" and it is indeed the first step. I offer Communist Czechoslovakia as a better example: look up Ketman, Havel's parallel society, paralelnipolis.cz etc.
3. Starting from economic opportunities. This approach sees the main problem in the lack of income opportunities for people without bank accounts. Resolve this and the culture will build itself.
4. technology - this: "carefully choosing and rejecting technologies based on their potential to control and surveil you" should be the start. Nostr is a great start. Building a replacement for Github is even better. But we need to go much further. Getting rid of DNS with something like DID would be a major achievement. The problem is that very few people are willing and able to go there.