You shouldn't worry about it, anything that's "w3m" is playable on the Frozen Throne BUT if you mean you want Frozen Throne stats for .w3m maps(for example, Frost Wyrms in Reign of Chaos have pierce attack, while in Frozen Throne, they have Magic), then go to "World Editor" then click "Scenerio", then click "Map Options" then you will see a something named "Game Data Set" below.
Go to it then click "Melee - Latest Patch" - This will convert settings to the latest Frozen Throne patch I think.