The handy DoubleCommand extension to OS X system preferences will swap Command and Option (Alt and Meta) keys, but that entails a manual operation twice per day.
Several free and paid apps will help automate changes when the OS X "Location" changes. Marco Polo works fine for my purposes and is free and GPL. Any of the Location-changing tools will do, since they will all open Applescript files.
That leaves the actual changing of the preferences. Apple doesn't make much Applescript-recordable software nowadays, so recording doesn't work. Instead, one must make OS X available to scripting via the Universal Access panel and then figure out the names of the GUI elements of interest.
To figure out the names of the GUI elements of interest in a OS X preference pane, use the free Apple tool UIElementInspector as described well at MakeUseOf.
Ok, if you read this far, you know how to do what I did. Here, then, are the Applescripts for turning a PC keyboard into a Mac keyboard, at least for swapping the Command & Option (Alt & Meta) keys.
The command for the PC keyboard location, name it "swapKeys.scpt" or something similar
tell application "System Events" if UI elements enabled is false then tell application "System Preferences" activate set current pane to pane id "com.apple.preference.universalaccess" display dialog "This script requires access for assistive evices be enabled." & return & return & "To continue, click the OK button and enter an administrative password in the forthcoming security dialog. (Then the switch will be set for you. You can always undo that change later in the System Preferences, 'Universal Access' pane.)" with icon 1 end tell set UI elements enabled to true if UI elements enabled is false then return "user cancelled" delay 1 end if end tell tell application "System Preferences" activate reveal (pane "DoubleCommand") end tell tell application "System Preferences" tell application "System Events" tell process "System Preferences" tell list 1 of window 1 set swapped to value of checkbox "Command Key acts as Option Key" as boolean if swapped is false then click checkbox "Command Key acts as Option Key" click checkbox "Option Key acts as Command Key" end if end tell tell window 1 click button "Activate" end tell end tell end tell quit end tell
The script for the OS X keyboard. Name it 'normalKeys.scpt' or something similar
tell application "System Events" if UI elements enabled is false then tell application "System Preferences" activate set current pane to pane id "com.apple.preference.universalaccess" display dialog "This script requires access for assistive evices be enabled." & return & return & "To continue, click the OK button and enter an administrative password in the forthcoming security dialog. (Then the switch will be set for you. You can always undo that change later in the System Preferences, 'Universal Access' pane.)" with icon 1 end tell set UI elements enabled to true if UI elements enabled is false then return "user cancelled" delay 1 end if end tell tell application "System Preferences" activate reveal (pane "DoubleCommand") end tell tell application "System Preferences" tell application "System Events" tell process "System Preferences" tell list 1 of window 1 set swapped to value of checkbox "Command Key acts as Option Key" as boolean if swapped is true then click checkbox "Command Key acts as Option Key" click checkbox "Option Key acts as Command Key" end if end tell tell window 1 click button "Activate" end tell end tell end tell quit end tell