Error: You are not registered as a developer
You meet error saying:" You are not registered as a developer." when you make changes for object/data type in T-code SE11.
For example, when you apply Note which requests manual corrections.
There is not enough authorization for the user. Without a developer key you won't be able to change the data type in T-code SE11.
The access key is given for developers, who are registered.
You may refer to Note 86161 for registering developers and objects.
Related SAP Notes
SAP Note 86161: Registering developers and objects