modifying creepers and custom ore spawns(?)

I have two questions, im gonna ask them in one tread.
1- How do i modify a creepers explosion power and fuse time? i know i can change those things when spawning the creeper but can i modify an existing one?
2- What is the most optimal way to implement a material that has its own set of tools n armor? like can i make a custom block using armor stands and make it replace ores and if yes, is it efficent? or are there any better ways?