Thank you so much for your kind reply.
I think "code fork" is what I want to accomplish.
How does one do it? I can't find much info on it on google
could you provide me any reference please ?

What I mean by mainnet is that people can join the mining network and just mine and
contribute to the network.

If code fork happens, can people just use regular bitcoin wallet (if it forked from bitcoin)
and bitcoin transaction website? Thank you.