Converting lines to shapes?

Hies all, this is my first post here, motivated by a doubt that's killing me.

I'm currently working with some vectorial cartoonish drawings, and while it's mostly quite easy, I'm having problems with disconnected lines. At the end of a disconnected line it needs to gradually get thinner and end in a small, rounded off point. It needs to to become thinner much slower than the normal rounded-off point, kind of a sharpenned edge effect.

So far the only method I could manage is making a shape instead of a line, but it's much harder to work whenever I want to change something, since I have to rework node by node. So I was wondering if there was a way to convert a line into a shape, so I can modify it all I want as a line, and then turn it into a shape and add the sharpened end.

Thanks in advance.