It varies a little depending on the type of item (base game + expansion content, Store content, and CC each being slightly different), but is generally simple once you know your way around the tools.

• Standard game content with S3OC or EasyCASP.
• Store content can be temporarily converted to .package to treat as CC, or MC can log the instance ID to use elsewhere.
• CC can be edited in S3OC or S3PE.

If you want to make the same changes to many things, you're also in luck that someone made a tutorial on bulk recategorising
This is where the instance ID would be used instead.