Nowadays in AEM 6.2, I found the way to create a metadata schema editor for Touch UI. This metadata schema is created under /conf/global/settings/dam/adminui-extension/metadataschema and until now works perfect, also we can apply this custom properties for only toa DAM folder that author can select.
However, we have a requirement to apply these changes in Classic UI, so I know that the asset editor by default in AEM exists under "/libs/dam/content/asseteditors". So we overlayed that path into the apps/ and in that way we can set values to the new properties created under asseteditors. But, the problem here is that the custom properties added applies also to ALL the assets that we have in our AEM instance, to all projects. We do not need this, because each AEM project has their own properties. So, I did a research and I found an option to create a "New Metadata Template", in Classic UI. But it seems that this only can be used to assign default values to existing properties, because I created the template with few properties that I want, for instance, title and description, but when I open an asset I see all properties that resides in the /libs/dam/content/asseteditors.
Is there a way to create a custom metadata editor for Classic UI that can apply only to a specific folder ?