Is there a way to open more than one map at once in GalaxyEdit? Or failing that, to open multiple instances of GalaxyEdit?

Yes. It's quite easy

Ctrl + O.
Select the map you want to open.
It opens.

Ctrl + O.
Select the other map you want to open.
It opens.
... but where's the other map you've opened, the first one ?

Go to: "Window" and look at the names listed at the bottom of the drop-down box.

There you go!

Aha! I thought it was something simple like that. Thanks.

No problem man!
Feel free to ask more dumb questions!

I can. And I will!

Are they any secret hotkeys to do this?

I thought there was Ctrl+Tab, but it doesn't seems to work.
Is there any way to open 2 Map Editors at once? It'd help me on some copy-pasting tasks. ;o

To ask dumb questions?

Any key I press.

Yes, there are hot keys to switch between the maps. The default keys are ctrl+F6 and ctrl+shift+F6. If you dislike these hotkeys you can to as follows (See attached images if can't find it)

1. File -> Configure Controls...
2. Find Window - next document
3. Find Window - previous document
4. re-map the hotkeys for them.

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