It's probably not too difficult to "jump over" Large Stone Walls either, if that's what you're after. Juggling the upgrade lines ought to do it. You know, under stone_wall swap

upgrades
{
large_stone_wall
}

to

upgrades
{
epic_stone_wall
}

and you'll probably have to remove the relevant epic_stone_wall line from the large_stone_wall upgrade part to prevent conflicts.

Although personally I'd then just leave out both.