Does anyone know if it is possible to assign a value to a number, say 1, that
when entered into a cell it will automatically change the formula in
corresponding cells. EG. If 1 = +10days
I enter 1 in b3, then the formual in b5 will change from +20days, to +10days
etc.

I don't even know if this is possible with excel, but would very much
appreciate any feedback possible. Thanks.

I don't think it is possible to assign a value to a number, you can only
assign a value to a cell. Also, your example refers to 2 cells, B3 and B5, is
it a typo?

However, why not use some available features of Excel, like using named
ranges?

Go to cell B3, then on the formula bar, on the left where B3 is written,
click it and put for example AddDays. Now, in your cell where you would like
to use the content of this cell, simply add at the end of the formula
+AddDays.

If this is not what you want, let us know!

Stephane.