Underscore between spaces?

I want a program, that I can add a underscore between spaces, if I want using a shortcut key ?

I believe this can be set up if you're typing a document using Word.

Underline text or spaces - Word - Office.com

I want this ability in any or all programs including explorer in windows7.

JerometheGiraff said:

I want this ability in any or all programs including explorer in windows7.

Globally, that's gonna be a tough one! I know for explorer a great cheap tool is "Better File Rename" (which I can't live without personally)

Better File Rename 5 - the better batch file renamer for windows

re you trying to get rid of spaces in filenames?
Like "My File Name.txt" becomes "My_File_Name.txt" or am I imagining it?

Yes I am. I want all file names to have a underscore no matter where in windows save a file or rename a file.

That's nice but I want it done for me automatically. Simple concept. If I hit <spacebar> make a underscore.