I'm not sure if i understood correctly, please correct me if i'm wrong:
1.- You resize a segment using Transform->Fixed Size->Scale Segment on. For example, resulting on a size of X:30, Y:10, Z:5
2.- Next, you want to add an empty space (padding) on X to the previous result, so apply a Transform->Fixed Size->Scale off, with X:35, Y:0, Z:0. That should result on a scaled segment of X:30+5 (space), Y:10, Z:5
If so, i'm afraid this is not possible. RailClone doesn't generate an intermediate mesh with the result of each transform, but combines each one of the operatores in sequence, and applies the final result to the segment mesh.
It works in this way for efficiency reasons, and to preserve instantiation.
In this case, 'Fixed Size' parameters are overriden by next Transforms. Specifically, X/Y/Z values are overriden when different from zero. But 'Scale Segment' parameter is overriden always, taking the value of the last transform.
It works similar to the Material operator. If you combine Mat ID 1->2 + Mat ID 2->3, it doesn't result in Mat ID 1->3, because material ID is not replaced in the mesh for each stage. Just values are overriden, taking the last operator.
I hope it has some sense.