Okay, I'm a noob with interfaces.

I have a child set up on my main interface window. I have two separate panes, one for the login and one for the map. How do I swap them at runtime?

Thanks in advance.
winset(player, "control", "left=[SomePane]")

You could also put right as the pane. If you set both right and left you get a splitter.
In response to ExPixel
I knew it had to be easy. Thanks ExPixel! (for the 100th time?)