Vim displaying normal keys like shift

Question

I want to map the key in Vim so that I hold the key, say, and then press another key, say b. And then holding a will change what pressing b does.
Just like we use shift, just with all the normal keyboard characters.

Is it possible? And if so, how?

Answer 1

The only way to do this is to turn it Ainto a regular modifier through xmodmapor the like, and the only vim modifiers support Ctrl, Altand Metatherefore, not only do you lose the normal functionality of the key, but you also add it to the set containing already one or more keys.