You cannot freely switch Time Machine backups from being network-attached to locally-attached. (*)
When backing up to the network, backups are stored in a per-machine disk image, of the form <hostname>_<MAC>.sparsebundle, stored at the root of the target volume. You'll see this file on your Time Machine disk.
Local backups, however, are stored in Backups.backupdb at the root of the target volume. If you open the sparse bundle, you'll notice that the internal structure of the disk image starts with the Backups.backupdb that I just mentioned.
(*) Thus, it might be possible to migrate the contents of a specific sparse bundle to a local volume using the following commands:
Code:
hdiutil attach -readonly -noautofsck -noverify \
'/Volumes/<BackupDisk>/<hostname>_<MAC>.sparsebundle' && \
sudo ditto \
'/Volumes/Backup of <hostname>/Backups.backupdb' \
'/Volumes/<BackupDisk>/Backups.backupdb'
If "Backups.backupdb" already exists on the <BackupDisk>, this likely won't work. If this does work, however, the next step would be to select the disk at its new location in the Time Machine preferences. Though the disk is the same, the network-attached and locally-attached variants will be aliased differently, for (hopefully) obvious reasons.
Unfortunately, being able to copy this information requires that <BackupDisk> be under 50% full, since it's effectively putting all your backed-up data on the volume twice. But this is the best help I can offer.