If you want to change the cutting angle, there are 2 possibilities:
the angle should become larger (i.e. more obtuse). This is the easy case. You can simply grind a micro bevel by hand.
however, if the angle is to become smaller, this does not work. As you can see in the sketch, a lot of material has to be removed for this (red arrow). Doing this by hand seems unreasonable to me personally. This takes me too long by hand even with a diamond plate, it's a case for the machine.
Fig: Overhang when reducing the cutting edge angle