Here's the 2013 LMGTE BOP history, with links to the officials docs, and brief commentary on GTE-Pro:
7 March - adjustments to the rear wing for all cars
22 May - 991, 997 gains 0.3 mm of restrictor; Vantage loses 10 kg
14 June - Corvette gains 10 kg; both Viper and Vantage lose 10 kg
19 July - both 991 and Vantage lose 0.3 mm of restrictor
1 October - Vantage loses 5 litres on tank capacity