|It sounds like you are asking Excel to divide a number by 1000 through the formatting feature. I don't think that's possible.|
You probably have to use another cell with a formula to divide the original number by 1000 and then format that cell the way you want.
Another option is a Worksheet_Change macro that divides the number entered by 1000 as soon as it is entered and then replaces the original number with the new value.
Maybe someone who is better with Custom Formatting will have a different idea, but I'm pretty sure you can't perform an operation on a number via any type of formatting.
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