ability to make custom prompt files without overwriting the lib one

[elsolo5000-2]

Is your feature request related to a problem? Please describe.
i wanted to be able to make custom prompts.py files without overwriting the original one.
the goal was to modify them as per model basis because all models do not respond the same tho the prompts.
i know there is system prompt option but i thinked to have more granularity

Describe the solution you'd like
add a "if custom_prompt.py... else use prompts.py

Is this not possible with the current options.
i tried monkeypatching without success but i am just an amateur

Describe alternatives you've considered
modify the file each times

Additional context
also i have another question, is there any reason why you use:
{{tool_descriptions}} and {tool_descriptions}
or we can modify the code to have the everything in double brackets or in single brackets