I have a document with lots of drawing done with brush tool, however, when I tried to increase the stroke size it creates undesirable results with each stroke ending/corners rounded etc. I thought that I would be able to change the stroke settings to change the stroke caps and corners, but turns out you can't do that for brush tool? Just now I've found the pencil tool and it creates exactly the result I want, and I can change the stroke settings as I wish which is perfect. Is there any magic conversion method somewhere that would allow me to convert my brush stroke paths to pencil strokes? Or do I have to redraw all of them? :/
This kind of depends on which brush is used.
If the brush strokes are shapes with a fill you are out of luck. There's no direct conversion back to a centerline path. There are some tricks to try and work around to a centerline again, but I suspect those may be more trouble than simply redrawing.
If the brush strokes are still merely stroked paths, just remove the brush stroke...
Select the paths, and in the Brush Panel click the Basic "brush".
Basic isn't really a brush. It really means "basic path", i.e. no brush applied.
From that point you should have standard paths (like those you'd create with the Pencil Tool) where you can alter stroke weights, profiles, etc.