I'm not sure if there is a term for what I'm looking for already that would lead me to the answer, so apologies if this is asked previously.
What I'm searching for is whether there is a way to 'mark' a cell (or a set of cells) from across the sheet/workbook, such that I can perform operations on these easily later.
The real world application of this is that I have built a 2 year budget, but some costs are potentially not going to be incurred, and thus this budget becomes "free-able". I would like to be able to mark these cells in some way and then easily add up the total freeable cash elsewhere.
The only way I could think to do this would be the colour the cells a particular colour, and then build some sort of IF/SUM that adds up a cell if it is coloured a particular hex value or similar, however from a bit of googling it appears that Sheets isn't capable of knowing what colour a cell is for use in a calculation. Almost a kind of 'inverse conditional formatting'?
If this approach doesn't work, there any other way of 'marking' these cells such that I can easily identify and count them later?