I agree that if you really need to up-pot (like if the pot is falling over), drop into a larger pot and fill in with more medium. It's too late to do anything that disturbs roots. (And these don't mind if they are crowded.) If the medium is somewhat broken down with the potential to stay wet (but not now, far too soon to give them any water) it also doesn't really matter - in active growth you also can't over-water them... not only are they hungry but they are thirsty. I use time-release fertilizer because when they're in active growth they're really hungry, and my fertilizing isn't all that consistent.
You can quite safely wait to "really repot" until next fall when they go dormant. The oldest roots (in the bad medium) will be dying anyway, that's just what they do. At that point you can remove the old medium and the old dead roots. But for now, it's fine, those new little sprouts are just starting. You need to resist the temptation to water. (Put your hands in your pockets if you are tempted to reach for the watering can
) No water until the new roots are 10 cm or so, and the new leaves have started to spread out. It is better to wait a bit longer than necessary to start to water than it is to start too soon.