Welcome to the forum!
Are you looking to make like hatchmark type of thing? Like if you were drawing with a real pencil, and you went back and forth, to make something like shading? If that's the case, we have a great feature for that. (LPE - Live Path Effect - there are many, but there's one called Hatches for this particular effect).
If that's not it, then the next fastest way I can think, would be to draw all the objects first. Then you can select all the nodes which you need to change, and change them all at once. You would still have to adjust the node handles, one at a time, though.
Oh, or here's another idea. Not sure if it would work, since I don't know how you have draw the path to begin with. But if you could draw the path with fewer nodes, you might be able to change the node type, and not have to adjust the handles. I'm not sure though.
Could you give us some more info about how the paths are created to begin with?
Another option might be to draw the smooth node with the Pen tool, and adjust the handle "on the fly". With the Pen tool, a single click creates a corner node, and a "click-drag" creates a smooth node, and adjusts the curve all at the same time. For me, it's tricky to manipulate, and I've never gained good skill with it. But others are really good at it!
