The Volunteer Service Team is appointed and serves at International Council's pleasure. However, every biennium International Council reviews each current VST member and accepts applications for those who would like to serve on the VST. At that time, International Council decides whether to keep a VST member in her current position, move her into another position, and see where new candidates could properly fit within the volunteer structure.
This is normal operating procedure; I'm sure International Council isn't planning on replacing all 100+ VST positions! That would be pandemonium!
Hope this clarifies!