First of all, you would setup widgets in your global rackspace to control your desired parameters.
After you have your widgets, you will find “Global Parameter Assignment” under the advanced tab. Assign each widget its own number.
Create a rackspace that uses your desired global FX. Create a widget to control your desired parameter.
In the mapping for this parameter, select “From Global Rackspace” and find the assignment you mapped preciously.
Now you can control global rackspace parameters on a rackspace per rackspace basis.