Guild Wars 2

My magicfind set (explorer) will be replaced by the assassins stat combo , i can choose new stats or i can choose only one stat ?

Existing magic find gear will allow you to select the stat combination you want when the patch comes out. Explorer’s gear made after the patch won’t exist and will be Assassin’s instead.

from explorer i can choose power thoughness and vitality?

It’s not known what exact stat combinations you can choose from. They only previewed legendaries, which could choose from all current combinations.

From thenews post

For example, if you have an Explorer’s Pearl Staff, you can now double-click it to change it to any other crafting stat. Since all weapons, armor, and trinkets with magic find will become account bound, any of these items currently on the Trading Post will be return to the poster. The only exceptions to this rule are in some high-end weapons that will still get the ability to select their stats, but will remain tradable.