If I'm not mistaken, the National Museum is okay with it as long as you don't use flash. I mean...siguro naman you've seen people post selfies especially w/ the Spoliarium hahaha. The San Agustin Museum also allows flashless photography. Sayang the CCP Building is under renovation...most (if not all) of their exhibition rooms and galleries allow photos pa naman. Would have been a nice one to visit sana.