Condition in same cell as formula

[cloud2828]

How can I create a condition relating to the cell that the formula is written in without getting a circular reference? Let's say I have a formula in A1 and it is said to return the letter in B2. How can I make it such that "If the letter in A1 is "Z", replace it with "X" instead" in the A1 cell?

Edit: Basically what I'm trying to achieve is a priority list such that certain letters should override others based on that priority list. So let's say I have a table with 2 columns, one that is the letter and the other is the cell where the letter goes and information can be override, if I was to put "A" in the first column and "A1" in the second column then in the next line of the table say "B" in the first column and "A1" in the second column and I want "B" to override "A" how can I get this done?

 

[Sam_D_Ben]

You want to replace "A" with "B".

Excel 2013/2016
	A	B
1	Column1	Column2
2	A	A1
3	B	A1
Sheet1

Muz

 

[cloud2828]

You want to replace "A" with "B".

Excel 2013/2016

	A	B
1	Column1	Column2
2	A	A1
3	B	A1

<tbody>
</tbody>

Sheet1​

Muz

I want to replace "A" with any letter I decide to write the condition for, but yes, for this example I want to replace "A" with "B". I don't see any formulas, just the table you posted. Also, the table shouldnt be in A1 because that's where the letters are going, the table it just the input.

 

[Sam_D_Ben]

Could you please share your condition.

Muz