Lastly what is a modified weapon?
I call a modified weapon - or better weapon with a modifier - any weapon that has an additional name to it, like dark, frosty, different material, etc... that changes the properties of that weapon, whether it may be price, speed, damage, requirements, etc..
I agree that a certain weapon skill should be needed to master a sword making skill, same applies to armor. I also think that maybe certain stats are needed to repair certain items, i just don't think it makes much sense for nonmagical weapons to not be able to hold it in your hand when you can already carry it in your backpack. A magical weapon can always have a spell on it that requires certain stats to be able to hold it properly.
On the other hand one could argue that equipping means to be able to hold the weapon properly, i.e. wield it. But then I don't think equipping should be needed in all cases for repairing an item.