With the sws extensions you get 5 slots for saving and restoring time selections. That means you can make a time selection, store it in slot 1, change your time selection, and then restore it to get it back. to run these actions, go to actions/show action list and put "sws time" in the filter. Or assign them to a keybaord shortcut. For example I always use a time selection slot for the length of the song I want to render (when I want to leave some space at the beginning or end for example), then when coming back to the project I do some work, restore the time selection before rendering and the song has the exact same length. The slots are saved with the project.