So i was thinking, i know its not so great, but this could really come in handy on occasions.
Make it so that you can remove 1 level of a skill and gain half of the xp back that it took to gain the skill.
for instance. i place to level 2 mining but i actually want 1 mining and 1 other skill instead for now but i dont wish to go out there and kill all those zombies again for it. so what i can do is remove level 2 mining back to level 1 and gain the 200 xp back from the 400 xp it cost to gain that skill, than i can buy level 1 and 2 of back packing.
just a thought that could work but still makes it so downgrading doesn't give a full refund atall give not such a good benefit.