Are there any cards capable of modifying the mana symbols?
You cannot change the actual mana symbols; however there are cards that would allow you spend mana "as though" it were another color. Mycosynth Lattice is one example. Among other things, it has:


  Players may spend mana as though it were mana of any color.


With this in play, you could spend any color of mana to activate Shivan Dragon's ability.

Celestial Dawn would allow you to spend white mana as though it were any color; Sunglasses of Urza allows you to spend white mana specifically as though it were red mana.

Sleight of Mind would allow you to change the text of Crimson Hellkite; it refers to "red mana"; so you can change that text to something like "white mana".

Note that in general; gaining access to other colors of mana is called "mana fixing". It can be in the form of lands or other objects that can add multiple colors of mana; or objects that allow you to spend one type of mana to get another type. You can read all about it here: https://mtg.gamepedia.com/Mana_fixing.