I vaguely remember reading that Donald E. Knuth has frozen the codebase except for actual errors in function that cannot be worked around reliably. His versioning system is a key to what his thoughts on this matter were, his popular projects have version numbers that approach (but can never reach) various trancendental numbers.
Then as mentioned there is no point in rocking a seaworthy boat.
Also we should try and get in Donald's head where he offered bounties for finding errors in his books (of which he paid out some $2.56 cheques of which most were framed and not cashed). He was a pragmatic perfectionist. Do what need to be done to get the job done but no more, the version numbers would keep getting longer if the code was tinkered with endlessly which will discourage random tinkering.
TeX was just Donald's way of getting presentable typesetting for his own books that could no longer be served by Hot metal typesetting and hand tuned equations. We should be thankful that he has had a lot of foresight many of us would have run past blindly.