I always test cheque layouts on Adagio's sample data or a copy of the live data.

If you want to use the sample data, you will need to copy the cheque layout file from your live data to the AP sample data. Then change the file extension to SAM. You can do both of these things with Windows Explorer.

When you are finished testing and modifying, you copy the cheque file back to your live data. Remember to delete the old one and change the file extension from SAM to your actual one.