[Gibbon1]

There is a mathematical technique called simulated annealing.

https://en.wikipedia.org/wiki/Simulated_annealing

The idea is code goes through development cycles. You have the most leeway to make changes in the first few development cycles. But less and less as time goes on. And the beginning of a development cycle you can make larger changes than at the end. Between cycles the code is frozen and you never touch it unless you can prove a change is needed. And development cycles are triggered by the need to for gross functional changes or interface changes.

[somewhereoutth]

Good analogy. Where I am we try to follow this process for each release cycle - so big changes early, then becoming increasingly conservative as to what gets altered/added as the release date approaches.