How to disable iMessage on a Mac remotely?

Hello,

My rMBP using Mavericks got Image Retention problems, so I took it to an authorized repair center for them to fix the problem. I erased all of the content, and reinstalled OS X Mavericks. On setup, it asked me about my Apple ID, and I logged in.

So, I left my MBP at the repair center, and then I realized that I should have logged off from iCloud

The problem is that I don't want my information (iCloud, iMessage, Facetime) to be synced (I don't really know if logging in to iCloud also logges in to iMessage on Mavericks). Basically I don't want them to read my iMessages, for example, for very obvious reasons.

Then I decided to change my Apple ID password. Is this enough to prevent iMessage and iCloud to sync? Using Find My Mac is not possible since I changed my password, and cannot rechange to the previous.

Thanks in advance.