May I save entity as variable and use this variable to refer this entity in unlinked procedures?

I'm deeply sorry if exist similar topic - I honestly tried to find something similar, but English is foreign to me and I have problems with understanding sense of problems which I found instead answer to my question(s)...

Can I save one particular entity as a variable and use this variable in another procedures? How may I do it?

And same question about turning one particular Player to variable.

Or maybe exist another way refer to a previously involved entity? 

Oh, and another one question I just remeber. Does it possible make animated armor texture? (Can animate only items of armor, but want texture of armor model. I made an animation but couldn't embed it to mod)

I searched the entire internet one year ago, but to no avail... 

Thanks for attention! Hope u can help