What is the correct pronunciation of 辫发？
According to Xinhua Zidian, the only admitted standard pronounciation currently for 发 (in Mainland) is


fā, various meanings e.g. "to send out, to dispatch", "to start", "to grow, to expand", "to open, to reveal, to invent", "to show", "to produce, to happen"; and
fà, meaning "hair".


As 发 in 辫发 refers to hair, it should be pronounced biànfà in Mainland China. This is also how I pronounce the word (native speaker).

In Taiwan, as indicated by the other answer, fǎ is correct.