Weapons can be customized by adding and removing components such as sights, stocks, grips, blades, etc. Also includes magical customization, such as enchantments and curses, and any others.
The first video game about Weapon customization was released in 2000.
Customizations may actually degrade certain traits of the weapons rather than only improving certain aspect.
Temporary enhancements should not count for this. Such as coating a blade with poison, casting a short-lived spell on the weapon that wears off in a few seconds or minutes, using some skill that temporarily boosts some weapon stats, and so on.