Sounds like unnecessary work if it is just the ca3.mnu file that is broken.

A repair install should resore missing files, so I would try just to delete the ca3.mnu file from your data directory, and then run a repair on character artist. That'll probably restore that file. If that works, you'll want to do a re-install of the latest update after that.

The Humble Bundle setup is a very good starting point, giving you everything you really need.

But if you want to expand the styles you have available to you, Symbol Set 4 and 5 offers a very nice dungeon and city style. Symbol set 1 is also nice for additional overland styles.

And you can get tons of new styles through the annuals. I love the annuals for their diversity.

You can use :CC2EDIT: on it.

Note that it can be a bit difficult to target the edge of the red x image, the actual edge seems to be a bit inside the visual edge, into the gray area. (Note that you can "spam-click" this command. Since left button repeats the command, and the command ends whenever you click with a non-valid selection, just keep clicking will reactive the command for another try)

Atlas will be down for a few hours due to network maintenance.

Well, according to the description, they are .png images, so those should be fully importable as symbols.

They are isometric though, so they won't work alongside other DD3 stuff, they'll basically be their own style.