I am attempting to use my Select+ Companion coupons (expiring end of month) for an upcoming trip.
AGRInsider - you may be of most help here

2 Questions:
1) It says they must be reserved at the same time - does that mean I can modify an existing reservation at the window, rebook it to a new reservation, and add on the coupon?
2) Does the new reservation for the companion go to a seperate itenerary or is it combined with the other onto one itenerary?