How do you plan before small software changes?

I have some extremely iterative approach where I change one function or one variable at a time, like a headless chicken. I am not planning beforehand which modules or functions I need to change but start from somewhere and like a linked list, I am moving on until the end.

But I feel like it is wasting my time. What is your approach when you want to have let's say -50 line of code changes?

say YOLO and jump right in.

I try to find a direct path through all the function calls et cetera which I need to change, then I just go over it from top to bottom, basically like yours.

It's a stable way to do it and I see nothing wrong with it.

At our place, we tend to build disposable prototypes to get an understanding of the design we're going to go with at first, and then let the tests drive out the real design when doing the implementation.
The tests then tell me which methods we actually need to change/call differently. Refactoring and DRYing up generally increases the number of method's touched.

Have been experimenting with refactor first and refactor last to make PR's bitesized as possible which has been going well.
Who wants to review a complicated 100+ file PR vs. a few unambiguous 5 file PRs

I just do them.

Just accept the scope creep and rewrite the project