So guys Ive discovered that Niner (from the companion mod "Niner") will not always wear what I give him. He likes to alternate his gear out so every now and then he will wear the awesome armor I so generously give to him but most the time he is just wearing his normal looking Niner gear. Is there anyway to make it so all he wears is what i gave him?

The most right way to do it is open his .esp file in GECK and uncheck all items in his inventory as his property (I don't know how this function called in english sorry). Then You'll be able to get all his clothes from his inventory and give him exactly what You want him to wear.

I think it might be because of how Someguy made him..
He'll randomly switch outfits at times, with the above post, it might be tricky, he might wear your armor, then switch to another set..

It seems like he'll switch to other armors, for instance like the quest where you go to the Vault 21 hotel, and he gives you a new set of clothing to go along with his..

And when he confronts you at the Mojave Outpost, and switches over to the NCR armor, and makes you equip it, to glue in some kind of speaker that plays music.

my niner just broke at Mojave outpost and after he gets to the radio he runs to freeside its really weird