A few questions from a complete beginner to VRTK (and certainly no Unity expert).
I'm modifying a Unity application which is based on VRTK v3.3.0.
vrtk 4 is completely a rewrite. You cannot modify a vrtk3.3 project to work with vrtk v4. The whole process is now dependent on using the prefabs directly with the camera rigs instead of creating SDK's.