Example:

SQLConnection.DriverName := 'DBXL4MySQL';
  SQLConnection.LibraryName := 'dbx4mysql.dll;
  SQLConnection.VendorLib := 'notused.dll';
  SQLConnection.GetDriverFunc := 'getSQLDriverDBXL4Mysql';
  SQLConnection.Params.Clear;
  SQLConnection.Params.Add('User_Name=root');
  SQLConnection.Params.Add('Password=secret');
  SQLConnection.Params.Add('HostName=localhost');
  SQLConnection.Params.Add('Database=mysql');
  SQLConnection.Open;

There is no difference when working with the client library compared to the standard driver, except for the fact that the custom parameters would be ignored when using the client library.