Jerry W. Lewis wrote:

A cell formula does not have memory. The only way to build in memory is
with VBA (You chould have a worksheet change event that updates the cell
when there is a change in the cell).

If it's a one-time change (eg subtracting an offset from data), it is
possible to use the "Paste Special" command.

1. Type the number to be subtracted/added in one cell.
2. Copy this cell.
3. Highlight the cell/range to be modified.
4. Use "Paste Special" (either right-click, or Edit-Paste Special)
5. Select the operation to be performed.