Are you on CC or an earlier version? In CC, your custom schemas are saved here: Documents/Adobe/Premiere Pro/7.0/Profile-<USERNAME>/Metadata Preferences. The path was different in earlier version, and I can't recall what it was. But searching the computer for the name of one of your schemata should take you straight to them.
I advise proceeding with caution as far as renaming or deleting custom schemas. After messing with one of mine, I ran into a crash on launch loading the project that was open when I created the schema. The crash did not repro in two subsequent tests, so at this point I suspect its unrelated to renaming the schema. Still, thought I should warn you...
Yes, I am using CC, and thank you! I was able to find the Metadata Preferences file. Oddly, only 2 of my custom schemas were represented by name in the file, but then I am not familiar the .xmp coding at all. Because of that, I will heed your warning and will not attempt to edit that file.
Are there no other solutions? What if I uninstalled the cloud and re-installed it? Would that remove the schemas?
I eventually determined that the crash I encountered in the course of this testing was unrelated to messing with the custom metadata schemata. What you could do is move everything from the Metadata Preferences folder somewhere else. If you hit any problems, simply moving them back home should get things straightened back out.
And upon further investigation of where custom metadata settings are saved, I found that my prior answer told only half the story.
- When you customize which metadata properties are the displayed in the Project or Metadata panel and then click Save Settings, the resulting prefs are saved to the path I cited above.
- When you click New Schema (and presumably add custom properties to that custom schema), that gets saved to a completely different path, which is used by other Adobe apps as well.
- on Windows: C:\Users\<USERNAME>\AppData\Roaming\Adobe\XMP\Custom File Info Panels\4.0\custom
- on Mac: Users/<USERNAME>/Library/Application Support/Adobe/XMP/Custom File Info Panels/4.0/custom
In limited testing of moving and renaming the Custom Schema, I ran into no problems. Again, if you save a complete copy of that folder's contents, then it should be safe to try whatever you like.
Bear in mind, though, that if you've entered data in a custom property and subsequently do something that prevents Premiere from finding that property or its parent schema, you'll no longer be able to view that data in Premiere.
As of August 2014, I'm not finding the files in the above locations... I am finding the xml file on Mac in Users/ <USERNAME> / Documents / Adobe / Premiere Pro / 8.0 / Profile-<USERNAME> / Metadata Preferences / <FILENAME>.xml
EDIT: Oops... wrong file. Ignore this post! That is the schema settings file, when, on the same screen you save the set as a preset.