The setting don't allow the user to change the 'hold breath' button currently set to alt. Is there some other way I can reconfigure this key? I'd like to change it to mouse 4.

Thank you,

What kind of mouse do you have?

For example, I have a logitch g700s and use their mouse and keyboard program to make my mouse button 4 alt so Im able to press that instead of the actual alt key.

Check to see if your mouse has similar options. If it doesnt try googling your mouse to see if you can do the same thing out of game through windows.