I want to create my first set of personal Mods / Patches

[Apexcode1990]

I have a great grass mod and some city overhauls, Specifically Wildlands Renewal Ground Cover and Landscape improvement (Grass) and Thuldar's Ivarstead (City Overhaul).

Problem is that the grass mod is growing grass in some unwanted areas in Ivarstead mod. Now I have installed a few grass limiter plugins that remedy this to some degree and I could install another that would completely remedy the issue however, it  would also drastically cut back on the grass mods capabilities and coverage which I don't want.

So I'd really like to learn how to take these two plugins and create a patch that would manually remove some of the stubborn grass but leave the rest of skyrim intact. There are also some areas around whiterun, like grass inside streams where it shouldn't be that I would like to manually remove. Problem is that I have no idea how to do that specifically or where to start.

Would anyone be so kind to offer some great beginners guides, tips, videos on how to accomplish this?