All of these are have already been done in some fashion.
- You are correct that recoloring or editing these is more difficult than with standard animations. However, it has been done, this hack has a recolored Fire Dragon, and I myself have a recolored Demon King in my hack. Sacred Echoes has a completely custom Duma sprite using the system that FE8 uses for Fomortiis.
- This has also been done and there are several FE8 hacks that use this animation, such as An Unexpected Caller and Cerulean Crescent.
- Although direct source ports have not generally been done (with the exception of again Sacred Echoes, which ported Forblaze, among other things), these spells have been replicated in the commonly used custom spell engine, and so are available.