Professional :: Changing A Font Across The Frames

I have created an animation where I have pictures and text accompanying the pictures sliding in and out. However, I want to change the font of the text across the entire animation. What is the easiest way to do this? I have found when I have tried it, (changing the font in the text box) that sometimes it throws the whole animation out for each key frame that has that text (if this makes any sense). In other words, suppose I change the font in keyframe 1, the change it at the next keyframe, sometimes the second keyframe is no longer consistent with the first, perhaps only slightly and therefore the animation can run a bit choppy as it goes from keyframe to keyframe.