What you are doing is replacing existing abilities with new abilities.
Skill retraining allows you to move 4 ranks in ANY skill to a skill that is a class skill for ANY of your current classes. It doesn't matter if you originally bought the source skill as class or cross class ranks.
You could take a level rogue (for the skillpoints) at first level, fill up the rogue class skills, then take other classes and move the bought ranks over to your new class skills at 4 ranks per level.
The endresult is, technically, an illegal character.
