Allow JSON defined variations of existing blocks

[Barhandar]

For example, I'd like to have Railcraft's blocks (bloodstained, quarried, abyssal...) to be chiselable without having to install a mod or wait for updates. Or any arbitrary set of decorative blocks, such as Botania's metamorphic stones, or MFR's bricks.

[tterrag1098]

This is planned, but at the moment you can add variations with ModTweaker.

[Yulife]

Documentation for it if you need it!