Edit review controls.

gistfile1.php

<?php

remove_all_filters( 'group_buying_template_checkout/review-controls.php' );
add_filter( 'group_buying_template_checkout/review-controls.php', 'new_paypal_controls' );
function new_paypal_controls() {
  echo '<div class="checkout-controls">
		<input type="hidden" name="" value="'.Group_Buying_Offsite_Processors::CHECKOUT_ACTION.'">
		<input class="form-submit submit checkout_next_step" type="submit" value="'.gb__( 'NEW!' ).'" name="gb_checkout_button" />
	</div>';
}