Totally possible. I had to do this when I tried to dual boot Windows 7 with Mac OS X, the Windows 7 was botched so I just deleted the partition it was on and the dragged the Mac partition to fill in the free space. A little time later I was good to go.
As for resizing when transferring to a different drives, this works all the time when I transfer my 16 GB SSD
install to an 8 GB USB drive. (I have an install 7 GB or smaller so it fits no matter which one.) All I do is use the Restore tab in Disk Utility, set my Mac partition on the SSD
as the Source and the Mac-formatted partition on my USB drive as the destination. The OS automatically adjusts for the size of the disk, in fact almost doesn't know that a transfer has happened! Then when I want to transfer it back (going backwards with the above steps) it automatically adjusts to the free space available on the SSD
. The only thing to keep in mind is that you need to reinstall DellEFI each time you transfer disks, and will need to boot the first time with DellMiniBoot.