Protect IF statement AND allow data entry

Is there any way to setup a cell to allow data to be entered while not deleting a formula or conditional statement?

I have a series of cells that are added and if it reaches 300, I want it to automatically populate the cell with the number 300...otherwise, the user can enter the number themselves without destroying the statement for use again the following week.

Also, can I use a conditional statement to move an entire row of data? If a sum of numbers reaches 300 in the middle of my spreadsheet, can I have it automatically copy the values to the bottom of my sheet or better yet, another page and then clear the row for use again?

Thanks for any help you can provide.

Hi Stilton. This is how I have achieved this sort of situation. It may not be a total fix for you. I have a cell, W9, that contains a formula in it. In cell N9, I use data validation and use this setup: Under Allow: I select List, under Source: I put =W9, and on the Error Alert Tab I uncheck the Show error alert box. So now, I can type whatever I want in N9, and when I want to revert to the formula I use the dropdown on the data validation and select it.
Good Luck.
Squeaky.