Swords of Prosperity are an artifact human/elf daisho. They currently cannot be altered. However, there is already is a Gargish Daisho base weapon. Therefore, shouldn't the Swords of Prosperity be alterable into a Gargish version?
When SA launched very few of the human/elf weapons had a statistically identical gargoyle version of the weapon. At that time a decision was made to not allow the legacy artifacts to be altered due to potentially creating some overpowered artifacts. We now have many more statistically identical gargoyle weapons.
We have discussed the possibility of allowing alteration of the legacy artifacts that have a suitable gargoyle version. We are currently discussing how we would want to implement a change like this.