That's.... not what china did. They removed term limits (which russia already didn't have), allowing the current president to keep getting re-elected.
Well, Xi is probably the most powerful politician in China since Mao, so it was tantamount to letting him be president for life.
As for Russia, there are term limits on the Presidency--no more than two consecutive terms (but no limit on total terms). It's why Putin spent some time as Prime Minister while Medvedev was President. (During which time, you may recall, the Prime Minister of Russia was decidedly more powerful than the President.)