Thank you for the review!
I can understand how that might be tedious. The Ability to drag items between slots after originally assigning them to a character at the start of a level is actually a bug. I thought that I fixed it earlier, but it turns out that I only removed the dragging animation. By the time we caught the bug, there wasn't enough time to fix and before submitting the game.
The intended behavior is for you to have to strategically decide which abilities go to which character at the start of each level, and be unable to change that later on. If we add more abilities, then we can design puzzles where figuring out which abilities go to which characters is an integral part of finding the solution.
Unfortunately, this bug found its way into the game and we didn't have enough time to implement more abilities. We'll update the game and fix that after the jam.