I think that refers specifically to content bought from itunes, to prevent iDevices syncing with different libraries.
I am pretty sure you can configure iTunes not to sync, then plug in the iPad and maka a backup.
OK so I followed this process:
installed iTunes on new PC
started iTunes
clicked edit preferences, device, tickt prevent itunes from auto syncing
connected iPad
clicked store, authorise this computer
right clicked on device. clicked transfer purchases from this device
once completed I checked apps, tv progams, films and music and they were all copied over
I then right clicked on iPad and selected backup
then right clicked on device and select restore
once finished i checked the apps, films, music was synced which they were.
However at this point the photos are not synced. I can see the photos in camera roll via explorer but not the other albums.
When I go back and click on Edit / Preferences / Devices and un-check the box next to Prevent your iPod etc I get the message:
"The iPad "ipad name" is synced with another iTunes library. Do you want to erase this iPad and sync with this iTunes library?
An iPad can be synced with only one iTunes library at a time. Erasing and syncing replaces the contents of this iPad with the contents of this iTunes library."
and two click options "Erase and Sync" or "Cancel"
If I click erase and sync nothing really happens evberything stays on the iPad and the apps, tv progams, films and music are on the new PC.
However when I enable photo sync I get the message
"Replace the synced photos on the iPad "ipad name"?
This iPad contains photos synced with another photo library or folder. Photos and albums on "ipad name" will be replaced with photos and albums from this computer. Photos taken with "ipad name" will not be affected.
and the click option "replace photos" or "cancel"