Migrate user custom fields to another instance


I’m about to embark on a migration of a complex category and associated subcategories from one self-hosted Discourse instance to another. What is the best way to move over data stored in User Customised Fields?

I still haven’t decided which tool to use:

  1. Topic and Category Export/Import
  2. How to merge two Discourse sites

The first looks much easier but will result in the loss of a lot of richness / PMs, etc. And I’ve got no idea what will happen to UCFs with either - are the ‘donor’ ones preserved in a merger?

Thanks for your help and advice!