The parameter overrides on the Arnold Procedural object UI are stored in the BaseContainer between the id 10000 and 20000 with an offset of 100. The first override starts at 10000, the second at 10100, etc. The following IDs are used.
Here's a simple script to list the Selection expression of all parameter overrides.
To add new overrides you just have to modify the BaseContainer of the object.
Look at this script how to read and modify all types of parameter overrides.