Hi Siddharth!
You're halfway there, but the first step would be to use the alter_semantics hook. You'd use the $name variable to determine for what library H5P is about to render the editor (in $major_version and $minor_version). The $semantics variable will contain the complete editor structure that you can parse for the text elements that you'd like to alter - and when you have found them, you simple amend its tag property with the values that you want and are allowed to use. It's not specific to moodle, but works the same way on WordPress and Drupal.
All the best for finding solutions to your challenges! I don't know what the chances are, but I created the code to solve the SVG one just yesterday and filed in a pull-request.
Cheers,
Oliver
Oliver