Attempting to control process parameters in your car with undocumented features by trial and error? Highly advice against it. Who knows what can happen, you might even accidentally send accelerator pedal request. On the systems I've worked on you can absolutely not control the cruise control by externally firing CAN messages onto the wire. Sure, the engine would probably respond to them but it would also respond to the real messages being sent from the ecu in charge milliseconds later, causing very jerky response. You could also cause the cruise to activate at standstill or other non allowed conditions since those conditions aren't necessarily located in the engine ecu.
Something that looks like a valid parameter on the bus, by simple sniffing and correlation, might not be what you think it is either. It might sound strange but it's actually very common for a signal in a message to bounce through several devices before it is considered valid and is picked up by the receiver. For example the first device might output the raw sensor data almost straight from the A/D-converter, the second device applies an LP-filter on it and sends it in another message, a third ecu applies some condition on the signal and forwards it differently if those conditions are valid and finally a fourth ecu is used just as gateway to transform the signal into another can-message because the receiving device is from a third party that doesn't support the standard message format for that parameter type. And I haven't even mentioned gateway between multiple can-networks yet. Even with system documentation it can be hard to know what a signals does.
Something that looks like a valid parameter on the bus, by simple sniffing and correlation, might not be what you think it is either. It might sound strange but it's actually very common for a signal in a message to bounce through several devices before it is considered valid and is picked up by the receiver. For example the first device might output the raw sensor data almost straight from the A/D-converter, the second device applies an LP-filter on it and sends it in another message, a third ecu applies some condition on the signal and forwards it differently if those conditions are valid and finally a fourth ecu is used just as gateway to transform the signal into another can-message because the receiving device is from a third party that doesn't support the standard message format for that parameter type. And I haven't even mentioned gateway between multiple can-networks yet. Even with system documentation it can be hard to know what a signals does.