Instead of going off to China and founding the Shanghai Foreign Arms Corps (and later the Ever Victorious Army of the Qing), Fredrick Townshend Ward followed up his career as a French-trained Filibusterer mercenary under the infamous William Walker by enlisting in the Union army in the opening year of the American Civil War. Rising through the enlisted ranks and even recieving a field commission through fearless front-line leadership and bombastic self-promotion, Colonel Ward fulfilled the energizing role Lincoln desperately wanted for the army (but could not find in his slow and steady commanders, Ulysses S. Grant dying in the 1861 in this timeline) and made brigadier general in the last desperate days before the Confederacy was sufficiently pacified. He cashed his story of meteoric rise and glorious self-sacrifice (having been shot numerous times throughout the war) in for a political career and eventually became president of the United States.
Or that is, since in reality he left for Shanghai in 1859, maybe in this timeline he somehow managed to get into the officer training and was thus on his way for a shortened curriculum and quick commission at the onset of the war in '61. Anyways, the end result is the same. Ward; whether simply a famous colonel, a field-trained brigadier general, or a properly trained commander; is a Union hero of the war and takes the place of Grant (who isn't an officer due to some homing anti-redundancy butterflies between 59 and 61) as war hero turned president (though presumably taking longer to build up a political career than Grant had to).
How could this general guideline be improved and what might the effects of the mercenary-officer-President on American (and world?) history be?