Seems to me the solution is to dry up the rewards for taking the violent option and dangle incentives before the players to do something other than that.

Killing that room of stormtroopers will yield the player a lot of exhausted weapons, Stormtrooper thermal detonators with unlabeled buttons, and maybe a pair of binders.

But if they find a way to bluff their way through the room they can get into the lab before the blast doors close, meet up with the rebel agent, and blast their way out with the corvette prototype they can use as a getaway vehicle.

Even better if they can charm their way into convincing the empire to escort said ship out and to the hyperspace point- a duty reward for a clean getaway.

Perhaps I should have provided a better example. This behavior has cost them thousands upon thousands of gold pieces, (I'm no Monty Haul GM) brought a few of their characters to the brink of death, cost them opportunities, cost them allies, cost them magical equipment, and there are multiple locations where the party can never show themselves again for fear of total annihilation by the survivors of their antics. Their behavior hasn't cost them their lives yet, but it's cost them everything but.

Are they aware of all they have lost or given up due to their actions? Have they had those magic items lost or taken away from them? Or have they bypassed opportunities they may not have been aware of?

Do they have any reasons to lament not being able to return to those locations that they've angered?

Have they had any reason to regret losing those allies?

A TPK may be a bit extreme, but killing one or two players, when it is clear that they wouldn't have died if they hadn't taken the course(s) of action that they did (if they had those allies, or items, or could take the route through this territory instead of having to navigate around it for fear of reprisals to their earlier actions) that might help illustrate the problem with being murder-hobos.

Maybe it can be an issue of attrition--they find themselves not welcomed anywhere, unable to find an inn to get some rest, a shopkeeper to buy their plunder, nor to sell them the supplies they require, no one willing to take them on for a job. They could find that they have run out of sources of employment, any income other than plunder, and nowhere to exchange what they have plundered for equipment they actually want or need. Remember, activities don't occur in isolation--people talk, word gets out, and reputations develop. If every town they come across shutters itself to them, or worse, meets their very arrival with violence, how will they react? If you take this tact, make sure to make it clear why they're receiving the sort of reception that they have. Wanted posters, overheard conversations, flat out refusals citing information known about the players (I've heard about you; you killed my friend/family member/pet; I've been ordered to turn you away...).

Even most criminal organizations maintain some degree of order, and may not welcome such violently reckless people as your players seem to be playing.

How to wean them off murder... remember the cardinal rule of crime: there is always a witness. (Some little kid with a cell phone and digital zoom hiding in a tree, a pinhole security camera in the gate, etc., etc.)

My favorite band of cinematic murderers is Xena, the Warrior Princess's merc band. In the series prequel episodes, she's a happy murdering general until one day she happens to pick up a baby and snaps and decides to atone for the rest of her life (Adds Motivation, Protect the Weak). (I forget the exact plot where there were other pushes, but that works.) Perhaps you could work with one of your characters to do something similar. Then with another one to play the other merc who just couldn't give up the violence and had to die a sacrificing hero's death. Or the character who had tried to give it up but it didn't work out (Rambo, any number of other types), until the others helped him try again. Or...