How to pronounce words with double fourth tones? So I know for certain words, such as 不对, the fourth tone changes, but I believe 不 may be a special case. 

Some words such as  部队 seem uncomfortable to pronounce if I strictly follow 4th and 4th tones, but saying words such as 汉字, don't feel as uncomfortable. 

Is there a general rule (or at least a general rule with a few exceptions), for pronouncing double fourth tone words?
Yes, 不 is a special case. Other consecutive fourth tone morphemes are all pronounced (事件, 现在, 俱乐部), unless the word formed itself is a special case where the tone of the last morpheme is neutralized (看见, 用处, 味道).