How to create custom live template functions?

Hi,

I'm trying to use live templates in my plugin, however I would need to have my own custom variable functions (such as these). I found a post on here saying to use the Macro class and MacroFactory.register(), however that post was from 2007 and it seems the register method doesn't exist anymore.

Can someone please advise me on how I can make variable functions, even though to my understanding they aren't OpenAPI?

Thanks,
Alex