worksheet change with if criteria VBA!!!!!!!!!!

Hi,
How do I add VBA code to individually format a cell in a range of cells from k5:bb500 to track changes when users have amended or added a new cell entry.
Basically i have a list of dates in column k whereby it defines when I have locked down resource dates that have been requested. If a user tries to change or enter a new value in the range I need the code to work only if the date in column K in the same row is < Today()
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