I think there is no API but as far as I've noticed Architect is generally only a Client for Rules DB updates.
You can pretty easy check what DB activities are under Architect actions and then replicate them in your application.
You can run SQL Profiler on your rules DB, perform an action on architect and see what queries and in what order were executed on DB.
For creating PFs, properties etc. it's not a big deal to automate it using exactly the same queries as used by architect.
This is the approach I wanted to avoid. Typically no one guarentees the structure of the db schema and is subject to change without notice. But if the product has an API exposed then that is guarnteed to continue to work.