Everything is Mutable

In addition to _everything_ being [_awesome_](https://www.youtube.com/watch?v=StTqXEQ2l-Y), everything is also [_**mutable**_](https://en.wiktionary.org/wiki/mutable).

We need to _clearly_ define the process to changing things.
e.g. a decision that was made which we now have more/updated information on and needs re-visiting.

Start by reviewing the existing start-here guide and the issue's example about revisiting decisions when new information appears. Identify where guidance about changing decisions belongs, then confirm that the process is clearly defined and covers that example.

Written by the indexing model from the issue text.