There is a third alternative - create a Document Custom Tag called GoogleMapsApiKey and put your API key there. This will be saved with your .gno and used by default for your Reports from that .gno file. There are other posts on this forum that deal with how to create Document Custom Tags.
GoogleMapsApiKey
For completeness I also include some screen grabs for the first method, i.e. using Config Params dialog, as requested by palentino
Make sure Config Params dialog will be displayed:
Then click the Generate button to run the Report scripts and display the Configuration Settings dialog.
scroll down to the Google Maps Settings area and paste your key over the default one.
Scroll to the bottom of the dialog and click the OK button.