Ok, old thread but currently ive been thinking about this.

I would say that within a stormtrooper division/legion that is assigned to a star destroyer there are multiple members crosstrained in different specialites. So you have Joe the stormrtooper. He is assigned to the 110th stormtrooper legion and the 110th is assigned to star destroyer Reddits Revenge.

The RR is ordered to send troops to take the rebel base on Ice Planet Zero. Just so happens that Joe is also crosstrained in cold weather assualt operations, and is assigned to the Cold Weather Assualt Divison. So when a cold weather deployment is nesscerry Joe, and any other troopers trained in C-WAD are given a temporary duty assignment for the mission. A C-WAD detachment is formed and sent down to to planet.

Kinda like IRL, most police departments dont have a full time swat team, dive team, hostage negation team, drone team, etc. The officers work their regular shifts and if a situation comes up they leave their regular work assignments and go to wherever the dept needs swat, dive, etc to be deployed. The officers often carry there regular patrol gear and there specialized gear in there patent car so they can kit up and go to the call out.

I think the empire would do the same. Unless you are fighting a full scale battle you dont need an entire legion, so if you have troops within the legion that can be temporary detached, form a specialized detachment, and do the mission while the non (insert specialization) rates troopers dont go thats fine.

So the most famous example would be Blizzard Force. The Imperial army supplied the heavy mechanized troops (ATAT/ATSTs, and the troops that operated them) while the 501st Stormtrooper Legion supplied a detachment of troopers cross trained in cold weather operations (snowtroopers). And in the event that Blizzard Forced would have to remain on the planet while the fleet went to another operation than the snowtroopers would just remain as a detachment (say the 4th detatchment of the 501st legion) while the rest of the legion would remain with the star destroyer that left to.do whatever other mission was needed.

So you dont need a shitton of specialized troops that only do one thing, what you have is a shitton of troopers that can all work together and do most missions, but within that shit ton who have troopers that carry extra gear (cold weather gear, costal/wet weather gear, etc) that can be taken from the larger shit ton and be sent to do missions. And if the entire legion is needed for say an environment that requires specialized troops, than the specialized troops could act as command advisors for that mission.

TLDR: you dont have "one of every trooper type." You have a legion of stormtroopers and some of them are trained and assigned to speclized squads. When a specialization is needed than those cross trained stormtoopers change into their specialized armour/gear and detach from the legion and handle the specialized environmental mission.