Please read the version details for updates, thank you.
I've seen a lot of sliders for legs for pony and 1.5, but I've yet to see one for Illustrious based models so I trained one on the base model.
Positive values increase leg length and negative values shorten it.
The effects are very slight so you can crank up the strength to +-10 easily. Beyond absolute values of 20 image quality begins to degrade.