MIDEAST MONEY-Saudi regulator limits valuation changes in accounting shift

* Listed Saudi firms to adopt IFRS by 2017 * IFRS rules could have allowed big swings in valuations * But regulator directs cost model to be retained initially * Impact uncertain for large, complex groups By Celine Aswad DUBAI, Oct 16 (Reuters) - Saudi Arabia's securities regulator has acted to prevent big swings in the valuations of companies' assets after they shift to new accounting standards next year. As part of efforts to bring the Saudi stock market into the global investing mainstream, t