You should never (well, hardly ever) enter a start or a finish date for a task.
Start date: Generally speaking (there are always exceptions) the start date is determined automagically by Project when you create links from the predecessor tasks.
Finish date: Generally spreaking (there are ... oh, wait I said that) the finish date is determined automagically by Project when you estimate the work and assign resources (or, on rare occasions, enter something in the Duration field).
So, in answer to the first part of your question -- there is a way to avoid entering start and finish dates: work with Project the way it is designed to work and do not enter the dates.
In answer to the second part of your question -- No but you can fake it. Insert the Start1 and Finish1 columns; copy the Start and Finish dates where you know them and paste them in the Start1 and Finish1 columns. Then, hide Start and Finish. Simple. Now all you have to do is remember that every time you update one of those Start1/Finish1 that you make the exact same change to Start/Finish. Or, if you change the Start/Finish fields or change something that impacts one of those fields that you update the Start1/Finish1 fields. If you have a perfect memory and never get distracted you can make Project do exactly what you want done.
Or, of course, you could use Project the way it is designed to be used and spend all that extra time actually running your project.
