I've never done it (still in the waiting period to get my first Makarov), but I think that's all you have to do.
But why would you want to? The 9x18 (9mm Makarov) is the original cartridge, it is slightly more powerful than a .380, you can get decent Russian ammo for about $5.50 a box (I bought 500 rounds from Dan's and it works fine in my FEG PA-63), you can buy hollow-point "premium" ammo if you want. Why spend the money and effort to downgrade your gun to an inferior but more expensive cartridge? Sure you may be able to find .380s at Walmart, but 9x18 isn't difficult to get. And for the cost of a replacement barrel, you could probably almost buy an FEG PA-63 and have two nice pistols that shoot 9x18.
Doug