Creating a custom text entry input source (keyboard layout) based on an existing one

Question

How can I create a modified copy of an existing text entry layout?

To be more specific, I'd like to add the parenthesis ( ) and # symbol to the Armenian (alternative phonetic) layout by sacrificing some other symbols.

I know about the possibility of mapping a key to a different one, but that won't work as I need this for one layout only. Also that would be rather a dirty hack.

Answer 1

Adding new custom keyboard layouts is pretty easy if you know what to do. There is already a detailed answer on how to set up a new keyboard layout. You will only need to add entries for the changes you need.