Modding Gold Weapons

Lets say i got a gold weapon, maybe a long sword with Fire Damage, +13% while hexed, and of Fortitude +20
Would adding my own modifiers like a zealous hilt and a pommel of swordsmanship destroy all mods on the sword? or just all of them BUT the extra damage mod?

It's an even exchange. If you put a new hilt on, the old one is destroyed. Everything else stays the same.

Alright good, now i can mod those other weapons i had....

Some gold weapons don't have a full set of mods automatically. Many of their properties are part of the weapon itself. For instance, I found a gold fiery scimitar that added +15 health, fire damage, 10% chance of something else and some other modifier on it. I pasted a pommel of shelter onto it and added some defense to it without sacrificing any of its abilities. Just try to upgrade and if you get the "Item X would replace existing Item X" just cancel it.