type
  TDataMod = class(TDataModule)
    Database: TDatabase;
  public
    procedure TempAlias(NewAlias, NewDir: string);
  end;

procedure TDataMod.TempAlias(NewAlias, NewDir: string);
begin
  with Session do
    if not IsAlias(NewAlias) then
    begin
      ConfigMode := cmSession; (* NewAlias будет ВРЕМЕННЫМ *)
      try
        AddStandardAlias(NewAlias, NewDir, 'PARADOX');
        Database.Close;
        Database.AliasName := NewAlias;
        Database.Open;
      finally
        ConfigMode := cmAll;
      end;
    end;
end;