solved. It seem that, not like written in the Documentation, the REST Connector resets complety (not overwriting just the parameter) after setting the new URL. So it was necessary to set all other Query Parameters again to get it working.
FROM JSON (wrap on) "root" PK "__KEY_root"
WITH CONNECTION (
QUERY "authorization" "Bearer",
QUERY "access_token" "$(vTOKEN)"
QUERY "other" "oldValue"