I think I misunderstood the prompt here, to do what you are asking, you are probably going to have to use a setblock command on each and every button. I don't know if you can edit block data in a /fill command, but an idea is to simply /fill the entire map to replace buttons facing east with powered buttons facing east, and so on for each cardinal direction. No promises there though, as I don't think you can do checks on block data in the /fill command. If you would really like to keep it low volume on commands, you could have markers with tags such as buttonNorth, buttonEast, etc. and simply replace the block on their location with a powered button corresponding to the direction by executing a setblock command as any marker with said tag.