This is the main way of getting newer, better weapons in the SO2RPG.  However, it's a little more specific than you saw in the original PSX game: "Customize" only refers to personalizing weapons forged from sharpened metal, or crafted from leather and similar materials.  

To improve on your weapon, you'll need something to attach to it, such as a very strong rare mineral.  Your success does depend on your level, but don't wory, failure will only depreciate the weapon a little bit (if at all) rather than leave you with a hunk of scrap metal.

Unlike the PSX game, in SO2RPG Machinery, firearms, and purely magical weapons like books can be improved with other skills.  It seems only fair that we allow books to be improved with Authoring and guns to be improved with Machinery. ^_^  The skill you use to improve your weapon is important in that it decides whether it will become stronger through magic or through technology.

Metalwork is similar to Customize, except it is instead used to forge armor and other useful items!  You can also improve upon your existing armor etc. to some degree, by adding on to them, but to get the strongest protection you really need to start from scratch with the best materials.

To improve upon armor or create accessory-type items, you'll need some sort of jewel mineral, like a Sapphire of Green Beryl.  On the other hand, starting from scratch requires a pure metal, like Damascus or Mithril.