I believe that the main idea of MDS repository is to keep schemas in a corporate way, independent of your project or specific needs, and I always saw the resources as unable to edit in Jdev too.
During development, I usually edit the schema in editor tool and than redeploy the xsd direct in Enterprise Manager (without the JDeveloper).
But, There must be a way to update/modify atleast file based mds artifacts in JDeveloper? Because the editors needed for XSD, WSDL, EDL are already there in JDev. So if a sub team wanted to play the role of MDS artifact Development, then JDev should provide a role for them. Just my opinion.
Although, it is not directly supported OOTB, but still you can do that in JDev. This is what I think, you should do in order to edit the MDS artifacts and then, deploy those to the Server.
(1) I assume, you already have a jar used for the MDS Deployment. This jar contains the MDS artifacts, you want to edit.
(2) Follow this Oracle article, which mentions how you can have a JDeveloper - MDS based deployment profile. Then, you can edit the MDS artifacts in JDeveloper and deploy those all also.
(3) But there is a catch here.. You'll always have the content edited by you. Imagine, another developer making changes to the XSD, then, the latest copy of that XSD won't be available in JDeveloper for edition. If you always want to have the latest copy of the MDS, then, I would suggest that you extract the MDS contents from the server (in the form of a jar) and use the same jar in Step 1.
Its a kinda long-shot, but..it is what it is :-)
Hope it helps !