Well, although I've never successfully changed ydk carbons, it looks do-able
Prise those two tabs vertical then the brass square plate should pop off. However, the coil cables will be soldered onto the back of them, and I'm not sure how much room you would have to play with.
I broke the spade terminals hooking up a Turbopower motor recently, and by chopping the coil cables off at the terminal, you can unwind them one turn to give you lots of slack
That's basically how it works on a simpler scale! On this motor the carbon housing is metal and connects inline further down. Principle seems the same though
Anyway, get the coil wire off, then snip the little braided copper wire off that comes out of the carbon. Re-solder the coil wire back onto wherever it goes.
Taking new carbons, which come with the spring too, you'll need to somehow thread the spring onto the string wire, then keeping the wire out a bit put the carbon in the holder, and wrestle the brass plate back on being careful not to pull the coil wire off. Then solder the braided cable to the back of the brass plate (you did keep that poking out didn't you?)
All the above is hypothetical. I nearly changed the carbons on a dc07 motor years ago but then got a good motor off a scrap machine do didn't bother. I might attempt it one day, but I cant solder so I'll need to persuade my stepdad to stand in the garage and soldering about a bit.
Maybe one of the mvacs techs have done it successfully?
However, how would you know that the buggared carbons havent killed the armature? I've seen Hoover motors with chunks taken out due to bad wear. I've heard of a commutar cleaner stick, but you would have to mount the motor, fire her up and push this stick against the armature to clean it up. If you uncover wear then it's game over anyway!
How would you know that that was sound under there?
Long and short of it, it's usually easier to get a scrap machine with a good motor, or a new motor from here, there or anywhere!