Can 'IF' condition be applied to the same Cell which already has value in it ?

Hi all,
Hope everything is fine.

Just for my explanation, I have attached a sample of the excel sheet. It has 'Before' & 'After' named sheets in it for better understanding.

I have certain values (Not in formula format) in individual cells. Is there any method where I can apply "IF" condition to those cells wherein values which are already present in the cells shouldn't be disturbed.
If there is a value of '0' or 'O' only then the value or the if condition has to be applied. For the rest, it should be as it is.

Till now I was doing like:
•I was adding a new column.
•Apply 'if' condition in the newly inserted column.
•Copy the obtained new values from the 'if' condition.
•Paste it back to the required column.
•Delete the column where I had appled 'if' condition.

Is there any alternate solution wherein no new column has to be added separately ? Formula must be added in the same column itself.

Example:
•) If in column 'A' or 'B', there is value '0' and in column 'A'or 'B' if the value is 'Y', then the new value after applying "IF" condition can be either 'Y' or 'N'.

•) If in column 'A' or 'B', there is value '0' and in column 'A' or 'B' if the value is 'N', then the new value after applying "IF" condition must be 'Y' only.

•) If in both the column, the values are '0' or 'O', then the value can be 'Y' & 'Y' or 'N' & 'Y' or 'Y' & 'N'. But not 'N' & 'N'.

In short,
Combination of 'N' & 'N' in both column 'A' & column 'B' must not be there if there is '0' or 'O' in any one of those 2 columns.

Thanks in advance.

Hi AliGW & CK76.
Thank you for the suggestion.

If you don't mind and if you are having some free time, can you give me a suggestion on the thread which I had posted yesterday ?
The thread is located in the below mentioned link:

https://www.excelforum.com/excel-gen...ent-value.html

Thanks in advance.