Hello Zombo;
When you say that Step 7 modifies your LAD into STL automatically, do you mean without your requesting it? Does it do it while you are programming, or do you see the changes when you open a file that you saved earlier? I have never seen that happen since I have version 5.x I think I remember something like that with version 3.3.
What version and which OS do you use?
Anyway, I am including an image that I prepared for an earlier post; it shows a simple LAD network, and its STL translation. Notice the jump-to-label instruction (jump if false) thast is inserted after the inital logic, and the "NOP 0" instruction if the RLO is false. These instructions are essential to translate from STL to LAD or FBD; they define the start and end of the graphic blocs used to show STL: instructions in other formats. They do not modify the STL logic (unless you count the microseconds needed to process them); they are only there as cosmetic help.
So you can insert these JNB (Label) and Label: NOP 0 liones in your STL: networks, and then request Step7 to go back to LAD view. It has to be done network by network, though. Good luck.
Hope this helps,
Daniel Chartier