Change part of a formula across many worksheets

How do I change part of a formula without changing the sheet reference?

I've tried grouping the sheets together when I make the change but then the sheet reference is changing as well..

Ex: When I change =SUM('09 OCT 10'!W65)+8 on Sheet2 (Named 09 OCT 10) to =SUM('09 OCT 10'!W65)+6, every sheet then references the 09 OCT 10 sheet. So far, I have been changing the formula in each sheet manually, but with 3 formulas on each sheet and 63 workbooks to change, there must be a better way.

Any help is welcome.