Does anyone have any experience with how well the CX computer system (and CX agents) handle multiple FF numbers?

I am flying YVR-JFK-YVR booked on a single itinerary and want to credit each segment to different FF accounts.
Current plan is to have the first segment sent in and have the agent enter the 2nd for automatic credit.

Is it too dangerous to ask them to put in one FF number for the outbound and to change to another for the inbound?