How-to: Mark edited lines
Is it possible in Notpad++ to mark edited lines?
I know this from other editors, like for example SynWrite - this draws on the left a thin line at each edited line.
Have a look at the “Location Navigate” plugin, it marks changed lines in orange and changed+saved lines in light green (these are the default colors, can be changed…).
[BTW, this is a 32-bit plugin with no 64-bit version available that I know of. So you need to be running 32-bit Notepad++ to use it.]