ofPath uses ofPolyline internally. If you call path.setMode(POLYLINE), you should be able to modify the vertices as I;ve said before because I think that the vertices of your path are the vertices inside the ofPolyline.
In any case, if you are using an IDE as xcode or visual studio code you should be able to put a debugger and check if the positon of the vertices was modified
essentially an ofPath is a series of commands. you can manipulate those comamnds. I believe when you call get tessellation or get outline on an ofPath you are getting a rendering of those commands into triangle mesh or polylines but that you can’t alter the ofPath that way.
As zach says an ofPath is composed by default by commands not by points. you can alter the commands using getCommands(), the to in each command is the most similar to the vertices in a polyline, although in cases like bezier, curve or circle that’s not exactly the case since to is only the last point of the bezier or curve segment or the center of a circle arc.
using POLYLINE mode as davide explains you can set the path to not use commnads and instead directly decompose them into polylines as you add them, in that case though you can’t really access the generated vertices for altering them since that could mess up some calculations in certain cases if you added more commands later on