The V-Ray materials list in the new Asset Editor is synched to match the Rhino scene materials each time a scene file is opened. This prevents V-Ray from overwriting any material changes introduced while V-Ray was not present (not loaded or installed).
Wipe Scene Tool
Found in Extensions > V-Ray > Tools, this new tool can purge the scene of all V-Ray related information. Additional functionality includes the optional removal of any unused Rhino materials and component definitions.
Randomize Scene Material ID's Tool
Found in V-Ray > Tools, this new tool allows you to assign a random color ID to your materials. This provides a workaround for materials from v2.0 scenes which all have black color IDs.
Randomize Object ID's Tool
Found in V-Ray > Tools, this new tool allows you to randomize of all existing object's ID numbers.
The method in which render quality is handled in V-Ray 3.4 has changed. This process is now much simpler and straight forward. The local Subdivs parameters in materials, lights and camera have been hidden and will no longer have an effect.