10% of a lesson is 4,5 minutes.
Which 4,5 minutes am I changing in every lesson?
10% of my teaching load is half of one class.
Which grade am I changing this year?
10% of the chapters in the textbook is 1 chapter.
Which topic am I changing this year?
Don’t try to change it all at once, decide which 10% you want to focus on this year and change that.