It's this possible?

Hello everyone!

I just made a list of changes that my hack will include, and I would like to know if they are possible to do and how much hacking they would need.

Here it's the list:

• Create a item to revive Leo and add him as a 15 playable character.
  
• Add a secret room at the Colosseum with a secret boss.
  
• Make the economizer only reduce mp consumption by 75%.
  
• Put the Dragons that were on Kefka's Tower in other locations.
  
• Add new bosses in the places where the Dragons used to be.
  
• Make the man in Narshe only give you the Ragnarok magicite and give you a hint about where it's the sword.
  
• Buff the final boss.
  
• Add some new weapons like Ice claws.
  

I wonder if this would fit on a expanded rom and if the expanded rom would cause bugs or glitches.