So let's say I've got an awesome particle simulation that I can comfortably preview as 1000-points but want to render as 1000000-points.

No problem, I can go to the emitter nodes and change the number back and forth manually depending on if I'm tweaking the sim or doing a render. But this is very manual and prone to error.

Or I could set up two takes, one for preview and one for render, and have the emitter parameters set to take-specific values. But if the values are part of a complicated expression that I might want to change, then I have to remember to change the expression in both takes, or split the expression into the common bit and a take-specific multiplier which is stored in a different parameter. Still feels kind of messy.

How do you typically handle this? Personally I'd love to see (maybe it exists?) a command to let me query if a cook was due to a display or render call. This way my particle emission could be controlled like:

if(cookReason()=ISPLAY,1000,1000000)

I used a pre/post render script on the ROP to set a variable/parameter.
Nodes can query this one to see what's going on.