how to enter a base value and an overide value on excel : Let me explain it with an example.

I'm pulling Sales data from a website and doing calculations on it, so that for instance I would have two columns:

Sales Company A | 15000 (from the website)
Sales Company B | 24000 (from the website)
-----------------------
Total           | sum()

I want to be able to override the sales so that it impacts the total, but not to lose the original value. So for instance I could change the company A sales manually on my cell, hit enter and get a new total. And if i made a mistake, i can just delete the company A sales and it will go back to the original 15000 (without the need to retrieve the data again i would hope).

Is this possible on excel? Or an addin or something that allows it?

