After doing some experiments, Sigma confirmed that decreasing the levels of one skill wouldn't be the same as acquiring experience with other skills. Still, while it wasn't perfect, it didn't take long for Sigma to think of a way to make good use of that new function.
After transferring all the experience from Rage to Regeneration, Sigma managed to make it that passive level up fast just by getting pissed. That was quite easy for him since he was always controlling his frustration due to the lack of results with his goal.
At the same time, after transferring the experience of Water Manipulation and Cold Resistance to other skills, Sigma was able to make them level up faster by making things cold around him. He basically increased by three hundred percent the mana/experience rate by. He felt that he could do more, but for now, he was satisfied with the result.
"What else can I do here?" Sigma thought while smirking.