Custom changes to standard maps & new content updates

What is the best practice around updating the standard maps? Especially when new content updates occur in the future ?

One of our SMEs recommends making z-copies of all standard maps, and then we make changes to the z-maps and leave the standard maps alone.

Questions:

1. Is this the best practice using z-copies? The How-to guide does not mention this step, and it seems to say to edit the map directly for extension fields.

2. What happens to enhanced mappings (based on standard content) when new content / upgrades occur ?

Appreciate any help ASAP.