After some studying, I think I finally,
finally found a way to edit the layers. It's actually very simple, which is surprising, since I was sitting around dumbfounded as to why I couldn't change the Diet Dr. Pepper layers at all.
Basically, up at the top of the screen is a little section that's labelled "Active Layers". There's a little button that says "Change". Click that.
Then, a little window pops up and asks you which layer you'd like to switch to. In this case, I picked CTF mode. Once you select what mode you want, close the little window.
And then, finally, select the CPs or whatever and move or rotate it wherever you want.
*Note: Unfortunately, I haven't had time to test this out. I've only tried CTF mode so far, but it looks like it works. I haven't tried any of the other modes, so I don't know if it works for sure.
Also, don't be mad at me if you guys already knew this; I only just found out about it. >.<