Rename home directory without causing double Time Machine backup I want to rename the my home directory (/Users/thisone), using this technique.

However, I just started using Time Machine, and with 200 GB of data in my home directory; what will happen?

Will the entire 200 GB have to be backed up again, because Time Machine doesn't understand that the data is the same since the home folder name changed?

If so, as a panic resort, can I tamper with the Time Machine backup, renaming the home folder there too? (I have only a single backup so far).

If so, how do I do this? I seem to remember that even with sudo, OS X objects to any change in the Time Machine folder.
I just tried enabling Time Machine on a VM, saving one snapshot, renaming the home directory, and saving another snapshot, and Time Machine did save a second copy of the whole home directory.

When I tried it again but used bypass to rename the home directory on the Time Machine volume before saving another snapshot, Time Machine did not save a second copy of the whole home directory.

So try running a command like this after you rename the home directory:

for f in /Volumes/*/Backups.backupdb/*/*/*/Users/oldname; do sudo /System/Library/Extensions/TMSafetyNet.kext/Helpers/bypass mv "$f" "${f%/*}/newname"; done