With regards to mapping the keys, yes its possible to do so, however, as somebody who regularly uses multiple Mac's I feel it makes more sense to stick with the "default" keys. Usually the key mapping is better for switching the windows button and alt button to map to option and command. To have control on the external keyboard = command, ,while the internal keyboard remained the same would be bonkers.
On windows the "main" shortcut key is ctrl where as on mac its command. When typing on the mac I spend a lot of time using my left thumb to move to hit the command button, and thus the closer the command button is to the right edge of the x the better. As you can see in the following chart Matias is Almost perfectly aligned with the right edge of the X as opposed to just about every other keyboard i've seen out there. For a mac user this makes the transition VERY easy. I'm currently typing on a Das Keyboard 4 on a mac at my office and although I'm used to the thumb travel distance I still MUCH prefer the Matias when using a mac.
Note that you can swap the modifier keys very easy in OS X. Go to the Keyboard pane of System Preferences, and click the ‘Modifier Keys...’ button:
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(http://i.imgur.com/nrl3My3.png)