It is certain that he will come.这个句子改为was certain that he would come可以吗

It is certain that he will come.这个句子改为was certain that he would come可以吗
第二个句子,It was certain that our football team would win the game.这个句子改为is
certain that our football team will win the game 还是有含有虚拟什么的不能改?另外两个句子为什么时态不同?