Question spells.h

I was wondering if anyone knows why the spells listed in spells.h like SPELL_DISPEL_GOOD have this by thier name:
/* Reserved Skill[] DO NOT CHANGE */

is it just because they use the file messages or is there another reason. I have found the need to change one of the spell definitions and I am just curious what are the reasons you shouldn't change them.

They are "reserved" in that they may be in use in world files (wands, scrolls, spec_procs, etc.).
If you are confident a particular spell isn't used in any world file, you can change it here. However, there's a lot of unused numbers, so I'd just add a new one instead. Just remember to raise NUM_SPELLS as well.

world files, ok thanks I forgot about that part thanks alot.