Hi @Idris1 and welcome to the forum!
A couple of things:
Regarding duplicating a rule, here’s an existing topic for that request that you can vote for:
The good news here is that it’s marked as “In Development” meaning that Asana is actively working on it!
So I renamed your post here to focus on the “duplicate a custom field” part of your request; hope that’s OK. Be sure to vote for it!
Also note this workaround:
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