You might wish to try The French Campaign in Portugal 1810-1811 An Account by Jean Jacques Pelet, Edited, translated, and annotated by Donald D. Horward. Pelet talks about the orders from Massena to his subordinate commanders to maintain discipline and order on pages 99 and 154 and also of Massena's censure of Junot for not doing so. I could look more into these memoirs for you, but the material is definitely there and Massena did issue the orders. He also took great pains to assemble provisions for his field army and garrisons. Interestingly, Pelet also has reports of the British way of handling the Portuguese which wasn't widely liked by the Portuguese civilians. It is an interesting memoir by one of the Titans.

Sincerely,
Kevin