Backup for downgrade from Mavericks to Snow Leopard on smaller Hard Drive? This Problem might be very specific.

After having been very happy with Snow Leopard for quite a while I am now seriously considering upgrading to Mavericks with my 2010 iMac.
I would however like to save a copy of the old system to be able to downgrade and get back to it without having trouble and without losing any data.

My system hard drive is 1 TB (460 GB used) and I have a Time Machine backup on an external hard drive. Of course I don't want to touch this backup device.

I have another 200 GB hard drive and I was thinking about creating a bootable clone of my system on this device that I could use to get back to Snow Leopard.
Of course 200 GB isn't enough space for a complete clone copy. But since I have the Time Machine backup I wouldn't necessarily need to backup my user data, and then I have only like 150 GB to backup. So in principle my system without the user data should fit on the smaller device.

Is there any (not too complicated) way to do such a backup? Can Carbon Copy Cloner do that?
It can be done but involves a lot of juggling.

Your best option would be to shrink your existing partition, create a new partition then install Mavericks into the new partition.
You need to boot into recovery mode (or from the Snow Leopard CD) to shrink the partition (using Disk Utility) as you cannot resize the active partition. You can copy existing data from the original partition during installation.