I'm still experimenting with this function, but as yet, I haven't worked out how to change the outfits and weapons of Companions.

My favorite thing to do with Companions was to customise their Inventory to add a more personal touch to the game.

The first step was to give them a more interesting outfit.

Cass was given Desert Ranger armor and a cowboy hat.

Veronica got Sierra Madre armor and a red baseball cap.

The next step was to select a weapon for them to use.

But so far, I haven't worked out how to remove their default outfits or weapons and replace them with whatever I might chose to give them.

And if I met an human NPC that I would deal with on a regular basis, I did the same thing with them to make them more interesting.

Sally in Fallout 3's Zetan DLC got a power armor undersuit, because I thought being in a more hazardous environment then other NPCs, it would be appropriate for her to wear armor, even if she never fought the enemy.

Most often, this required the use of console commands to remove whatever they had equipped as default so the game would force them to use whatever I equipped them with via inventory.

Does anyone know if I can still do these things in Fallout 4?

And how to do it?

I could make dogmeat wear dog armor and chain collar by giving him the items and select them in his inventory and hitting "T", on PC.

I didn't test it more, but, following that method, you should be able to make any companion wear outfits and other stuff.

"T" key only appears on wearable items by the companion, it seems.

Hope it helps!

Please note that if you decide to make them equip a weapon, as per the method in Grimkunu's post, you'll need to give them ammo as well!