Both are right! 政府事先没有制定制度 emphasize "time" , 政府没有事先制定制度 emphasize "they did not ..."

你好！ The order of these two sentences are both acceptable,becausee the position of negative adverb in Chinese is not fixed. The words following negative adverb is the real negative words.In the sentence "政府事先没有制定制度","制定制度" is the real negative words.That mens"did not set up a system ". But in the sentence"政府没有事先制定制度","事先"is the real negative words.That means "制定制度“ is not in advanced. "事前“ a noun,use as a adverbial modifier.eg:事前多做准备，事情会做得更好。 “事先” a noun,use as a adverbial modifier.eg:这件事我事先不知道。/我事先不知道这件事。 Difference:"事前“ means"事情发生之前，before something happen” '“事先”means “in advanced” and it is in common use,so when you are not sure which one is proper,I suggest you use "事先“.

both ok