What is some grammar rules that you've saw change?
Maybe even just recently. Over time? Over your life time?
One I found is that we now use one space after a period instead of two. It's not really a "rule" as I doubt people really notice unless they're a proofreader, but it's a more modern usage of punctuation.
"Gregg Shorthand had achieved the most extraordinary success ever attained by any system in the history of shorthand." John Robert Gregg, 1922