The VMP Property Editor plugin lets you change properties of all Volume Maps currently loaded in the Overlay dialog.
You can choose which properties you want to change and also specifically which maps you want to see overlayed:
Downloads
VMPsPropertyEditor 1.1 for BrainVoyager 20 and 21 (Mac OS X) (compiled on 10.10) for Windows 64-bit (09-10-18)
Please write to support AT brainvoyager DOT com in case you find any errors or have any suggestions!