Notepad++ Trying to add a character after ONLY the first space in each line

Try TextPad. You can record macros and then play them back. So record what you want to do for the first line and after you have completed the first line, leave your cursor at the begiing of the next line. Then just play the macro until the end of the file. Or just hold down the play macro key.

https://www.textpad.com/