I've been rolling with the X12 Plasmacaster mod since it came out last week; such a gorgeous piece of tech, even if it doesn't
quite seem 100% "lore friendly" (wrong era of scifi for the Fallout Aesthetic, really), quite impressive that they managed to get 'fire mode select' AND 'alt fire' working like that though - you can toggle between semi-auto and full-auto, and switch to the underslung grenade launcher, just with custom hotkeys.
Plasma carbine/shotgun/sniper rifle/smart rifle with alternative fire mode, custom 1st and 3rd person animations (including power armor) and hotkeyable functions.
www.nexusmods.com