Allowing a cell with a formula to also allow for user input.

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?

sample uploaded.
Hopefully that help clarify.

I don't know anything about VBA, so perhaps its time I learn...

Thanks guys for all the help.
I now just need to take the time to learn the basics of VBA.

And thanks tehneXus for proving to me that it is possible w/ the use of VBA.

(I seem to have messed-up my first/second reply, so here we go again):

TMShucks:

Your example file seems to function perfectly! (exactly as I described)
You even managed to hide the individual cell-functions from the user. (how?)

If you could explain in laymens terms what you did, that would be very helpful.
Otherwise I'll start picking away at that code trying to figure it out one bit at a time.

Even if you could just give me a broad: "this is what your file was originally, I did ____ to it". statement that would help me get started.
(or did you just do as you described in your first post?)

Hopefully I can learn what you did and apply it to my larger data-sheets.

Thanks!