Is it possible to edit the Galactic Readiness/Galaxy at War stats shown in the single-player War Terminal (e.g., using coalesced.bin)? If so, how?
Yes you can change it there is a guide on this site
The only problem though which is noted in the guide, is any assest already required will not change, so it is best for you to change them before starting. This will not change the % readiness from 50 to 100%, but you can triple the value of each war assest so you can easily have over 5000 for final mission.
Short answer: "no".
Long answer: readiness percentage is not available without online connection, thus i suspect it is not stored locally (on your PC). Thus you probably can't change it. Even if that's wrong, though, you still should not change it - as well as all other stats, such as amount of points you get from some war asset(s), - because you only can do it by editing game's resource files, which is clearly "hacking", is against ToU, so (at least theoretically) it can get you banned, could lead to glitches, etc. However, at least in theory, it is certainly possible to do, provided you have sufficient knowledge and skill. If you don't, though (which is likely since you asked this question), then please understand that it is highly likely that nobody would teach you - here in public, - how to hack the game. Which results in "Short answer" given above. Sorry...