A reformation is mostly subtraction. The parts of a business designed for a buyer who has moved on rarely announce themselves, because they still produce some result. They just produce less than they did, for more effort, and the decline is slow enough to be attributed to the market.
The register
The working method is to write them down before deciding anything. A legacy assumption register lists what the current system assumes about how buyers behave, and against each one, whether that assumption still holds. The exercise is uncomfortable because most of the assumptions were correct when they were made.
Keep, reform, retire
Every item gets one of three decisions and the decision is recorded with its reason. Recording the reason matters more than the decision. Six months later somebody will propose bringing a retired practice back, and the register is what makes that conversation short.
Useful tradition and obsolete control look similar from inside. The separating question is whether the practice serves the buyer or only the org chart.