I hope this isn't a total disaster.
I was just about to use media manager to output my project for delivery to the 'finishing house' to do final effects and graphics for my client and discovered that i have been working on a 24p timeline for the past week.

Any ideas to easily change it from 24p ProRes 1440x1080 to 30p ProRes 1280x720?

Here's what I would do:

Drop the whole file thing into Motion 30p project, resize, export and pray for the best. That is if your footage is shot in 24p.

Create a new timeline in the proper size and framerate.

Go to the old timeline, select all (cmd+A), copy (cmd+C), go to the new timeline, paste (cmd+V). Adjust size and aspect of each clip as needed (use open sync to make this easy), any effects or CC should be unaffected.

FCP will typically auto-resize your video and built-in effects, but things like still images will typically need particular attention.

Thanks guys . . . yeah, no easy way around it.
I found the best way for me was . . . after copying all clips; i go clip to clip hitting f to bring up original source and either replace or superimpose (if i have to copy all filters and effects over). Going in and changing aspect and such is a mouse click headache but probably the same as far as time/effort.

Hope i never miss that at the start of a project again.

Perfect timing for this thread. I'm experiencing a similar nightmare except I have several different formats and frame rates to calibrate.