Weapon modding

Ok I have never really modded weapons, and people always tell me when I ask for PCs that if I add x mod it will add a few K to the price, well how does modding work, because I remember when I first started playing I was afraid that applying a grip would erase all other mods because it cautioned me, saying it would replace previous mods. Just looking for some insight. Thanks!

Upgrading a mod on a weapon for sale rarely increases the value of the item as much as the cost of the mod itself.

For your grip example, applying a grip to a weapon will replace any grip that is currently on the weapon. Prefix mods will replace prefix mods and suffix mods will replace suffix mods.

Check this guide that will explain everything about modding weapons.

http://www.gwonline.net/page.php?p=125

It basically all prefix and suffix.