Question: Is there a formula I can use that will change all cells with one character to something else? 

For example, I have cells with single letters and no matter what the letter is I want that cell to contain the word Member.

**More Info:** I get spreadsheets that contain, up to 40,000 rows. Column B will have names in the cells. Every once in a while a column will just have an initial instead of a full name. I'm looking for a way to change every single cell containing only one single character to the word "Member." The cells that need to change could be any letter but no matter what that letter is, if it's just a single letter in a cell, it needs to change to the word "Member."

Answer: 
Your question is hard to understand. 
I’m guessing that you mean that you have a collection of cells (say, column A)
that contain text values like “” *(blank)*, `A`, `AA`, `AAA`, etc.,
and you want to display “” *(blank)*, `Member`, `AA`, `AAA`, etc. 
Try setting `B1` to

```
=IF(LEN(A1)=1, "Member", A1)

```

and then fill the appropriate part of column B with that formula (e.g., by dragging).
You say that you want to use a formula, but also that you want to “change … cells …”. 
This is a combination that generally doesn’t work. 
Here are three things that are feasible:

1. A formula to display a value in an additional column in which single-character values are replaced by “Member”.
2. A procedure to actually change the values in the cells.
3. A VBA subroutine to actually change the values in the cells.

The other answers that have been posted so far are variations of option 1.

If you want to do this just a few times, option 2 is probably less work than option 3. 
If you want to do it many times, option 3 is probably less work than option 2.

Here’s an option 2 solution for you: Select the data that you want to change
(in your specific case, this would be Column B). 
Bring up the “Find and Replace” dialog box (e.g., by typing `Ctrl`+`H`). 
For the “Find what” field, enter `?`.  For the “Replace with” field, enter `Member`. 
Check the “Match entire cell contents” checkbox.  Click on “Replace All”.