If I am making the Pugliese recipe from the bread bible on a regular basis, can I just reserve some dough from one batch (30%) to use in place of making the biga? If so what adjustments would I have to make ....I’m thinking that i would need to reduce the salt…anything else?  Also the recipe states that the biga can be made up to 3 days ahead.  Can I keep the old dough on hand for that length of time?  If I need to keep it longer that 3 days, do I need to do something to it to maintain it?  Thanks for any suggestions!

I wouldn’t mind knowing the answer to this myself!

Let’s see how close I can come to Rose when/if she replies.
In general I would say yes. If you refrigerate the dough a few days or even a week would be fine.
You must be aware however that the amount of yeast in the saved dough will not be as much as from the biga. So you may experience a longer first rise. I would save the dough portion after the first rise because that should be the highest concentration of yeast.
You will have to adjust the recipe somewhat for salt and water.
Given those caveats with a little experimentation this should work very well I encourage you to give it a try.