How to modify entity type response when OpenType="true" ?

[pankajagarwalMS20]

Though there is provision to add opentype attribute but I could not find tests for adding property dynamically. Can you help me with this feature in repo ? What we need is similar to link below -
https://devblogs.microsoft.com/odata/tutorial-sample-how-to-use-open-type-in-odata/

Thanks !