Nov 17 (Reuters) - Australia's Pendal Group and buyer Perpetual Ltd will tweak the buyout structure of their agreed-to A$2.34 billion ($1.58 billion) deal, reducing the cash component and hiking the stock component of the bid, the companies said on Thursday. ($1 = 1.4837 Australian dollars) (Reporting by Roushni Nair in Bengaluru; Editing by Krishna Chandra Eluri)