Hi betazero,  

Thank you for your feedback. After adding the custom folder path in Printer Support search path, all the plot style table can be listed in Plot dialog's plot style drop down. 

It's in Preferences dialog>Application>Printer Support File Path>Plot Style Table Search Path. 

Click + too add your custom folder path under the search path. 

And restart AutoCAD. 

If you already added the path, could you please give me more information about the issue "Setting a custom location for plot settings does not work. I have to copy my ctbs into the default directory. "

Thank you for your time! 

Cecilia 

Cecilia Bao
Senior QA of AutoCAD for Mac