Editing Galactic Readiness stats for single-player playthrough
Solution 1:
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.