Hi Nathan thanks for posting! If you have line connections switched on adding new steps to this diagram should not break your existing connections. You can check this from File>Page Settings>Line Settings (please see this section of our Work with Lines article for more information about this.) If you insert a new step between two previously added steps and you have line connections switched on your lines should automatically adjust to accommodate the new step:
To maintain the layout for sections of the diagram which will not be directly connected to the new steps I recommend using a selection box to move multiple shapes together. That should allow you to easily make adjustments to the layout (for example moving a group of shapes slightly to the left to accommodate some new steps in the middle of the chart) without needing to manually move every shape.
Hope this helps! Please feel free to let me know if you have any questions.