Unfortunately you cannot change the sound or subdivision of the pre-loaded click tracks as well as any MultiTrack or CustomMix in Playback.
If you want a custom click for either your tracks or just as a solo click track in Playback the best thing would be to import through MultiTracks Cloud. You can download the content and add your custom click using a DAW and export the tracks individually. Then zip and import into MultiTracks Cloud on your account page. For a custom click only track we recommend the above steps as well as a great site called Metronomer.com. There you can export a click in any time signature and then change the sounds as well as making it enough measures to last 10 minutes (which is the cloud limit).
For more information on how to import content into MultiTracks Cloud see: How To Upload Content Into MultiTracks Cloud Storage