// returns list of changed modules
static LS dm_changeAllInstancesOfLibID(S oldLibID, S newLibID) {
  if (eq(oldLibID, newLibID)) ret emptyList();
  LS l = splitAtSlash(newLibID);
  if (l(l) != 2) fail("Not a valid lib ID: " + quote(newLibID));
  LS list = dm_modulesWithLibID(oldLibID);
  for (S mod : list)
    dm_changeModuleLibID(mod, newLibID);
  ret list;
}