No, you can't steal his power armor. It's a part of him, and if you use console command to remove it, his body would be all stretchy. He has 2 armors in the game, and you will get his first power armor after Blind Betrayal by doing BoS quests far enough (You don't have to side with them to get his Power Armor). You can't get his second power armor no matter what, without console command.
after u finish the quest "Blind Betryal" u don't a second suit of power armor from elder maxon , it's really a t-60 set with "BoS Paladin" paint , which u can apply to any suit afterwards
That's the Blind Betrayal quest, after returning to Maxson, he should give you Danse's Power Armor he drops off.
Why kill Danse, it doesn't matter for the BoS and you get a nice companion with bonus. I have Danse in Sanctuary and suddenly the settlement was attacked by bunch of BoS folks. Funny to watch. None settlers died, but all BoS.
Cheers,
-Klevs
It's free equipment and caps, really. You won't accidentally aggro the BoS either by killing them. BoS equipments get a really nice price. Danse himself gives one of the best perks in the game (Not talking about MacCready's bugged perk which has been patched). I find it to be the best perk in the game since the game is literally crawling with synths, supermutants, and ghouls. It's a waste to kill him during that quest since you will lose 20% permanent damage forever.
Just keep playing the BOS quest line and you'll find his armor. He left it behind when he left the Prydwen. If you keep him alive instead of killing him, the next time you see him he's wearing a suit of X-01.