I did a little digging and managed to do this:

1. Create a new rule set and export it to a file.
2. Open the GPO_Aria.prules file and copy all of the <rule>.....</rule> sections out of it and paste them into my new file.
3. Import the new rule file into my score and assign it as needed.

This actually seems to work quite well. The rules for all instruments are in a single file and it appears to use a property <if instrument-id = "xxxxx"> to apply only the rules that are for the instrument in use.

My next question is how do I find out what the instrument id is for the new instruments so I can add more rules to the same file?

I posted this to Presonus support, but thought I would ask here as well.

Thanks!