If one wanted to charge the battery in the plane without having to remove it each time, can an arming plug also be used as a charging plug, or is it necessary to somehow wire in a charging plug as well?

An arming plug would not be enough -- you'd need a separate charging plug.

But occasionally LiPo batteries catch on fire when they're charging, after a crash, or just because.  The fire is sudden and vigorous, which would not give you time to get the battery out of the plane before Bad Things happened to it.  If the battery's out of the plane when it catches on fire, it only incinerates itself, not the plane.

So most people keep their batteries separate from their airframes, and consequently have them out of the airframe for charging.

I believe Igor never removes the battery.
And he is a world champion.

Greetings Robert-Jan

My Thunderpower 820 CD charger, by design, won't charge without the balance tap connected.

That aside, Merry Xmas !

I appreciate all the advice. I had seen in other posts that Igor charged the battery in the plane and thought it might be alright. It seems like there would be less wear and tear on the connections if you weren't taking it out and replacing it after each flight but I see the safety in charging outside the fuselage.