How to shift a domain without shorting a list

Hello,

I am creating a large tread (green) on a series on steps without shorting the existing list. I am currenting using sub-list to define the size of the tread but I want to shift it along the curve to define a specific location (red line).

Loose_Step_Guideline.gh (18.5 KB)

Here is a reference image of the the tread being shift further down the curve but remaining the original list size