Customisation for Comments

[goncholden]

Am using modus-vivendi theme to which I add a bold font for everything.

I want a special customisation for comments, using normal weight, and having a 
keybinding that changes the
contrast ratio between the comment colour and the background.

Had started writing a minor mode, but this seems to be a non-standard 
implementation. What would be the
appropriate way to customise comments as described. Any examples I can use?