Salix Pharmaceuticals, Ltd. (NASDAQ:SLXP) has backed out of a proposed Irish tax inversion with Italian firm Cosmo Pharmaceuticals S.p.A (SWX:COPN), taking a $25 million hit in the process, but also said the two companies will continue to do business together. Even though there hasn’t been any concrete move to change the rules around tax inversions, the fact that changes can be applied retroactively changes the calculation for any company thinking about a major reorganization done solely for tax purposes. “The changed political environment has created more uncertainty regarding the potential benefits we expected to achieve,” said Salix President and CEO Carolyn…