Stefan Goßner

Senior Escalation Engineer for SharePoint Products and Technologies

Guidance on modifying pre-defined content types has been published

Microsoft has published a whitepaper with an official guidance on modifying pre-defined content types.

You can find the white paper here:

The whitepaper includes possible alternatives for modifying the content types and also a list of known issues that can occur if pre-defined content types are modified.

The most important part is the conclusion:

We recommend that you do not change pre-defined content types in SharePoint Products and Technologies unless there is no other alternative. We recommend that you create new content types that are based on pre-defined content types, and change the new content types instead.