Change Style Tool
I'm coming from Samsung Notes that had a tool called the "Change Style" tool. I would click on this tool and select the new style (pen thickness, color, etc) that I want to apply. Then I would slide the tool across the stroke that I wish to change. I absolutely loved the feature and I think it would be really nice to have.
Consider the use case where I wish to change the color of a few words in my handwritten sentence. Right now I have to click on the lasso tool, draw a circle around the words, tap on the color option, and select the new color. Oops, my selection wasn't very accurate so it missed a few letters. Now I need to repeat the whole process again. Using the change style tool I could just run the tool over the leftover portion and my life would be so much easier.
Now consider if I also need to "bold" a few words. I would select the lasso tool, draw a circle around the word, and ... Oops! There's no option to change the stroke width. So now the only option is to decide on the pen width BEFORE writing anything. That's absolutely ridiculous!
Here's a YouTube video of the tool in action.
Nikhil Verma commented
I would also like to highlight the issue with the lasso tool. It's not clear which parts of the stroke are selected. Apple Notes solves this by morphing the circle to clearly indicate the selected section. Another way would be to highlight the selected strokes to make selection more precise.