You can hardly find a database design and development software that is as customizable as Toad Data Modeler.
Edit existing application forms and add to the forms:
Create new forms with input elements and use the custom forms in your macros.
Documentation is a part of the installation package. In the User Manual you can find seciton Customization - sample with detailed information about customization. A complete object reference is available also. Click Expert Mode -> Reference Guide to open CHM file with all objects, properties, methods and other useful data.