I did that, editing a player in franchise, but seems like it doesn't work as well. Let me explain, I created a player before franchise and all is well, meaning he is progressing in overall based on attribute gains. The edited player is regressing! He has pitched well, started 3 games and no runs allowed. However, he lost one point on overall so I looked to see why: minus 1 point on stamina, minus one point on arm accuracy, and minus 1 point for control on fastball, and minus 1 point for break on curve and splitter. He walked 2 batters in 18 innings, so no idea why the drop in arm accuracy from 65 to 64. His stamina was 83 so not expecting him to go more than 6 innings, which he's done in all 3 starts, but it dropped from 83 to 82.
While a tiny sample, it may be significant.