Hmm, you can use TerraCustom to generate a world that starts in hardmode and disable the "V" from generating during world creation. Though, I'm not sure if the "V" would later be triggered when you kill the Wall of Flesh for the first time in such a world, but it may be worth trying.
Another suggestion would be to use the hellevator generator item in the mod luiafk, so you can easily box out any Corruption/Crimson/Hallow areas.
Alternately (though possibly tediously so), you could use TEdit to manually edit your world to box in any Corruption/Crimson/Hallow, or even remove them completely, though depending how you do it, this could be rather time consuming.
I also wanted to point out one other thing (no mods needed), in case you didn't know it already (though it may not be exactly the kind of info you're looking for): killing Plantera, in hardmode, significantly slows down the spread of Corruption/Crimson/Hallow.