i saw, mark townsend already implemented the alternating formula
but you can find 2 new formulas in the ck.ulb folder

here is a short description:

1. Change
Let you define an iteration depth and a second formula to use from that iteration on

2. Blend
Let you define 2 formulas, and blend between them, this is a quite cool function, because
you can morph any fractal into any other fractal, give it a try