There are two ways to go with this. The way it SOUNDS like you're asking for is for your powered armor to carry an entire second set of ceramic plates all the time can be swapped in and out while you're fighting. I think this is a Bad Idea and I wouldn't equip MY armored minions this way. You're basically handicapping your troops by adding all that extra weight which basically kills your "interfere with other activities (shooting and running) as little as possible" criteria the moment they put the armor on.
The way that I think makes sense is to have support units embedded with your infantry so that as armor gets too damaged to continue those guys fall back just enough to get out of the heat of battle and have their plates swapped out by a quick-change system, and then go back to fighting.
There's all kinds of ways you can do this depending on how rapidly you want to turn around an individual soldier. The quickest way is to have a 'combat medic' who's embedded with your squad who carries a couple extra sets of plates, so your troops can just fall back just out of the thick of the fighting, have the plates replaced using the medic's special toolkit, and be back in the fray in a few minutes.
A more efficient way if you're envisioning brigade-level rather than squad-level combat would be to swap entire squads in and out of combat. This is a VERY old way of doing things that goes all the way back to Greek warfare where pitched battle was a process of constantly cycling your tired guys at the front of the formation back so they can get a drink of water and rest up for a bit while some fresh troops hold the shieldwall against the Persians or the Gauls or whoever.
In this scenario your squad would fight as a unit till they'd taken sufficient damage that they couldn't maintain anymore and then a fresh squad waiting behind them would move up and the damaged squad would fall back to an APC or something out of range of the thickest fighting and have all their damaged plates replaced at once, along with whatever medical attention was required.
In fact, there's no particular reason you couldn't combine both approaches. That's how I'd do it, if it were MY armored minions.