To be totally honest I get that message all the time. If you have signed in with the same Apple ID then you have nothing to worry about.
First, make sure you back up, and second, go ahead and sync what you need too.
If all else fails, get yourself a USB App on your iPad and transfer if over WiFi to your iPad. I use Avatrons
Air Sharing or get a dedicated Video App like
Air Video HD for $3.79 and either Download them over WiFi to the App, or with the Server on your Mac, watch them straight out of your iTunes library on your iPad. I have it and works without a flaw, and you can even set you streaming/download speed.
But honestly, there are so many Apps now on the App Store that can transfer over WiFi through your Safari browser using Bonjour its not funny. BUT if you need to go through iTunes, don't worry as it won't delete anything, as long as you are on the same iTunes ID . . . . Its just recognising it as a new Library because of the different IP address of the Mac . . . It Safe
Cheers