Possible Reversal of Data Validation

That's one of the problems with data validation you can delete it or destroy it by copy / paste into it. If you want to preserve data validation, you need to resort to VBA.

Maybe use regular formatting to highlight the cells (red?) to give some indication not to use them?

It would be better if I had something concrete to work with.

Please attach a sample workbook. Make sure there is just enough data to demonstrate your need. Include a BEFORE sheet and an AFTER sheet in the workbook if needed to show the process you're trying to complete or automate. Make sure your desired results are shown, mock them up manually if necessary.

Remember to desensitize the data.

Click on GO ADVANCED and then scroll down to Manage Attachments to open the upload window.