Does anyone know how to 'unlink' a pattern from a performance?

You can do so by linking the Pattern with a different Performance. Each Pattern can be linked to one Performance at a time.

From the Pattern screen:
Touch “Home”
Select the new Performance you would like to associate the Pattern with... then
Touch “Play/Rec”

The same Pattern is now unlinked and the name of your new Performance selection is showing as the new candidate.
Tap “Store Pattern and Perf Settings” to create the new link.

Once linked you can recall both by simply:
__ recalling the PATTERN by its location (highlight the Pattern Name and use the Data Dial to select the title)...
__ or you can go to [UTILITY] > “Contents” > “Load” > set “Content Type” = Pattern&Perf
__ or you can tap the Pattern Name box, see the pop-in menu, select “Load” to jump to the “Pattern&Perf” screen.

Extra Credit: Understanding your Sequence data like a Boss
_ Your Patterns and (MIDI) Songs remain in memory, even if you load in a different User File (.X7U).
_ There can be a maximum of 128 Patterns (Each w/8 Scenes and a Chain), and 128 MIDI Songs in their respective Folders. These are housed in the internal memory in Folders bearing the titles: Patterns and Songs.
Press [UTILITY] > “Contents” > “Data Utility” > dedicated Folder for internal memory.
_ If you create a Pattern Sequence or MIDI Song using the internal Sequencer, or if you load a .mid file to a MONTAGE Pattern or Song location, that data will remain in the internal folder until you either directly DELETE it, or you “Initialize All Data”... or you restore a complete BACKUP (.X7A).

_ When you load a User File .X7U, this action replaces all data in the following folders: Arp, Live Set, Motion Sequence, Performance, Waveforms.
_ Loading a new User file does NOT affect the Library, Pattern or Song folders. Their data remains unaffected by loading a new User File.
_ If you want to backup your sequence data externally (long term storage) you can either connect to your computer via MONTAGE CONNECT, then drag the contents of the Sequencer to your computer via the USB connection. Or you can SAVE AS... .MID File right within the MONTAGE Sequencer to a USB stick inserted to the “To Device” port.

How do I restore a single Performance, if it is not native to my currently loaded User Bank?
This is where the ability to capture and restore a Performance, using either the Soundmondo app, or by using the MONTAGE CONNECT application on your computer, becomes a useful workflow.

Once I have worked on creating a Performance (even while it is still in progress), I will capture a single bulk dump of that Performance data. This way, if I load in a different set of User Performances, I can quickly and easily bulk my latest work into the MONTAGE edit buffer. I can establish links between Pattern/Perf or Song/Perf. Then by pressing [STORE] I can include the updated data in with the just older User Bank. A quick Overwrite of that User File adds my new work to that older file.

John Melas’ Total Librarian is very useful for storing/retrieving Performances to/from a computer.