How can I interact with my running SPL application? E.g., if I want it to start or stop collecting certain stats, or if I want it to stop Export-ing certain properties?
In SPL, think about a stream whenever you need to send a message/data.
Create an input stream using a *Source operator (e.g., FileSource or UDPSource). When you want to interact with your running SPL application, send a message via that input source. The input stream operator will then send the message to a separate "parser" operator that can then act on the message.