First, you need to create area schemes. Then, create area plan views for each area scheme. Then define area boundaries, then do schedules for each scheme. Each scheme is independent, because each one serves a different purpose. I think the step you're missing is the first one.

after creating the new schemes as Alf just said, it's not wrong, this is exactly what to do to copy boundaries over and make your new areas. it seriously isn't a hard job if you isolate AB category (use a temporary VT). Dynamo should be able to do it easily also, might take some setup but once done you have it for future projects.

Thanks for the replies, but that's not really the issue.

This seems like such an obvious function to be hard coded - I don't understand why they've locked down the Area Type categories so much.

It must be VERY common for people to need GIA and NIA plans for virtually the same areas - same names, same numbers, etc... just slightly amended boundaries to calculate.

On creating totally 'new' areas for the NIA plans, I am now having to copy / paste all of the name and number information to the NIA areas - in a 30 storey tower!

You should have the ability to duplicate the areas plans and just change the area types.

Copy > paste aligned to selected views, will save a lot of time.
I'm actually working on a 30 storey tower right now and also we use similar (but not the same) boundary locations for differing area types.
I've worked on dozens of towers both resi and commercial and the majority of tall buildings do have repeating geometry throughout so you can definitely follow the architect's design formulas when copy/pasting area boundary lines to different levels. I would suggest starting on the most common level and copying up or down throughout the tower as needed, rather than copy say level 3 between area types, level 4 between types, level 5.....etc.

It may suck and you may hate it but that's how revit works right now and if you have any kind of deadline for your project you're gonna have to deal with Revit as it is, or start over in another software that does things exactly the way you need it to
You could start posting on Revit ideas if you haven't already, where you may start getting support of other users. Many things have been implemented this way.

Thanks Elton.

Very used to the 'how Revit works' limitations - this just seems like such an obvious flaw that could be easily resolved.

Kinda like why do we still use oil based fuels in our cars vs. so called "clean" electric cars using coal / diesel as their prime energy source, to both build and run the vehicles. LOL.

Certainly some things are frustrating AF within Revit, but I guess until someone writes a new program that does everything in everyway that everyone wants, we can only use what's available, or write our own addins / dynamo scripts. There have been huge gains in recent years for coders using Revit API's. This sentiment has been done to death countless times though, but it is what it is.

Dynamo could definitely speed up the process once scripted right for your project but i guess thats a skill vs time thing also.