Instead of making a new function I've tried using a property's setter function in a Godot Signal callback
Godot.Collections.Array sigParams = new Godot.Collections.Array();
LifespanTimer.Connect("timeout", this, nameof(PropName), sigParams);
However, this is throwing the error
E 0:00:01:0790 Error calling method from signal 'timeout': 'Node2D(SceneFile.tscn)::PropName': Method not found.
<C Source> core/object.cpp:1239 @ emit_signal()
So I guess I need a new function, unless there's another name for these setter functions.