To open your domain file in Lion, Mountain Lion or Mavericks or to switch between multiple domain files Cyclosaurus has provided us with the following script that you can make into an Applescript application with Script Editor. Open Script Editor, copy and paste the script below into Script Editor's window and save as an application.
do shell script"/usr/bin/defaults write com.apple.iWeb iWebDefaultsDocumentPath -boolean no"
delay 1
tell application "iWeb" to activate
You can download an already compiled version with this link: iWeb Switch Domain.
NOTE: Domain Cracker and iWeb Switch Domain are the same app. They both were created from the script above. You can either download the app from the switch above or create your own using Script Editor. If you download then it will be blocked by Apple's Gatekeeper so you'll have to approve it's opening.
Just launch the application, find and select the domain file in your Home/Library/Application Support/iWeb folder that you want to open and it will open with iWeb. It modifies the iWeb preference file each time it's launched so one can switch between domain files.
WARNING: iWeb Switch Domain will overwrite an existing Domain.sites2 file if you select to create a new domain in the same folder. So rename your domain files once they've been created to something other than the default name.
You need to be in your Home folder before you can see and use that checkbox. Your Home folder will have these folders in it: