Well, again, just guessing here based on your questions and what I've seen in your form....
If you want to use your form to work with existing list items, the first step is getting those list items in to your main data source. Since your main data source appears to have no repeating nodes, you'll need to add a repeating group. For simplicity's sake, I'd structure it the same as your 2DS with your existing ShP info.
Then, you could use qRules to copy your list data into your main data source using CopyTable - it is a pretty simple command to use.
From there, you could edit and submit items in your form. If you don't want to save that data in your main data source, you could use the delete command to remove it when the user submits. Then when you want to load it again, you could pull it from the list and copy it back into your main data source.
Of course, if you change your main data source, you'd need to re-do your mapping (which I know is kind of a pain - sorry about that....)