This thread is very old but still contains good information so will be maintained as Library reference.
The most important change since this thread last updated; The location of where Profiles are placed.
Under your metadata (Library/Application Support/Plex Media Server), create Profiles.
You place your customized profiles here now.
Copy the original / master copy here and edit appropriately or author fresh.
The files must be owned by plex.
Any changes you make require a restart to become active (Plex reads into memory at first use).
