When modifying objects of the same type in the Form editor, they first must be selected. Instead of selecting each button individually, it is possible to select them all at once using the Select Similar Objects command.
1. While in Design mode, click the Explorer button in the tool bar
2. Select Forms from the panel
3. Open a form to modify
4. Right click on an object (in Windows) or Control + click (in MacOS) to show the contextual menu
5. Choose the Select Similar Objects command
All objects of the same type are selected and ready for modification.