Customize "Make" button with add more selection inside of it

Continuing the discussion from How to add new "Make" selection for Quotation?:

I just want there is a way to add custom button by custom script and I got programming knowledge too. And I also know how to internally add python script into bench.

I just want to know what is the example of code syntax to add inside to the blue button “Make” instead of create a custom grey button beside it.

Any idea?

Bump into this request , just got the same request from my client . They would like to have a new custom doctype and allowed Opportunity to convert into .

So will need a make Button as mentioned on the previous link .