I am not aware of any Safari feature that permits site-specific assignment of a User Agent.

The following Applescript is a poor man's attempt to approximate such a feature. It prompts the user for an address (eg, 1 Infinite Loop, Cupertino, CA), then opens the address in a new Google Map window, and changes the User Agent to Google Chrome using the original script. Like the original script, it can be run either as a standalone application or from Safari's script menu. Incidentally, it would appear that any change to the User Agent remains in effect <u>only</u> for the current tab or window and is lost when that tab or window is closed.

-- Replace xxx in the following statement with the full HFS path to the User Agent-changing script, eg: "Macintosh HD:Users:username:Desktop:UserAgentChangeScript.app"
set pathToUserAgentScript to "xxx"
activate
set newURL to (display dialog "Enter a map address:" default answer "")'s text returned
tell application "Safari"
activate
make new document with properties {URL:"http://maps.google.com/maps?q=" & newURL}
end tell
run script file pathToUserAgentScript