Determine the pros/cons of different methods to handling renamed fields

[rileykarson]

We're not sure what the best approach to a renamed field is, and there are a lot of options- conditional reads, O+C, using CustomizeDiffs, etc. We should investigate the different options and write a summary of the pros/cons of different approaches, ideally forming a recommendation. That recommendation may differ if both fields are top level or if one or both fields are nested, if the field is forcenew, the field is a boolean and hard to use O+C with, has a default, etc.