Well, no new skills are possible as of now (and I believe they will never be), so you'll have to choose the one existing skill that you like most. Hammerdwarf or macedwarf are rather close to that. You can also edit it so that there will be "crowbardwarf" profession in game instead of "hammerdwarf", but skill will still be named Hammer.
Damage output is now being discussed in another thread on weapon research, but a quick answer is - yes, you can control the damage and the way it is inflicted very flexibly.
Hit rate is not moddable.
Excuse me sir, but, a crowbar is nothing like a mace or hammer when I wielded it.
It was like a sword or axe. B)
If you allow the weapons to be made by the civilizations that you want to make crowbars in the entity_default.txt file, they will be able to make it (from the forge).
And you can also modify some things that influence damage, but hit rate and pure damage is based upon the dwarf's stats and the materials the weapon is made of.
Also, if you wanted to see what it would look like, here's the item_weapons file.
[ITEM_WEAPON:ITEM_WEAPON_CROWBAR]
[NAME:crowbar:crowbars]
[SIZE:350]
[SKILL:SWORD]
[TWO_HANDED:37500]
[MINIMUM_SIZE:32500]
[MATERIAL_SIZE:3]
[ATTACK:EDGE:100:1500:swing:swings:sharp edge:2000]
[ATTACK:BLUNT:1000:4000:whack:whacks:flat edge:3000]