I wasn't sure how to write the title of this post, or whether or not the title actually applies to what I am trying to do...
but here is my scenario:

I have a spreadsheet that has a lot of cells that require user-input.
I want to have a master drop-down-selection cell (at the very beginning of the spreadsheet) that allows a user to select a "starting point".

The drop-down "starting-point" selection would pre-populate all of the spreadsheet cells,
then the user can go through and manipulate some of the pre-populated values to their liking.

Then (perhaps I'm getting ahead of myself here) I'd like the user to be able to go back to the master drop-down-selection cell and be able to choose a new "starting-point",
Which would then go back through the spreadsheet pre-populating over anything the user has manually input.

...

so basically:

User chooses a pre-populated starting-point.
User goes through and tweaks values he/she would like to tweak.
User looks at result... say's "hum, that's interesting..."
User can then go back and choose another pre-populated starting-point and start all over again.

...

Any ideas?