Require Data To Be Entered In Cell Unless Selecting Specific Cells

I came across a problem with my workbook where the best solution I can think of would be this:

I need to prevent data from being entered anywhere else on a worksheet unless Cell X1 receives data first - anywhere else, that is, except for Cells U6, O79, U86, O159, U166, and O239.

How do I edit my existing code to do this?

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Thank you so much! That did the trick!