Need help managing ISO backups! (+ partitions)

[/RaspberryPi]

I had got a 64GB SD card, a pi and a few other things from the university i attend, for a past project. They're not asking for any of it back so I figure I can just keep it to tinker around with.
I had a spare 256GB card so I copied the 64GB with win32diskimager but ran into some minor issues regarding the file it output (the pi boots fine on the new card though!).
The file is 64GB which isn't ideal, since I don't want to read / write the entire disk's worth of data every time I make a backup. Especially since I moved to a 256GB SD card... That would take forever. I can compress the file to what it should be (~7GB), but I don't want to compress and uncompress the images every time I have to flash a card

1. Is there a way to get ONLY the bits of data that are actually useful? I don't need to store the empty 50GB+...
2. I have a few folders in the image I'd like to remove. But the .IMG file doesn't let me delete them using 7z. Trying to extract -> delete -> remaking the img file doesn't work because I keep getting errors about the symlinks. Is there a way to alter the contents of an existing image?

I recently got ZFS working on the pi and I'd like to use it on a separate partition of the boot drive. I am fully aware that this isn't an ideal deployment, a single drive vdev only offers partial protection etc. I just want to get it working as a project, I already have a NAS server for proper data storage.
But there doesn't seem to be an easy way to shrink the current drive's partition and format the rest with ZFS. Am I missing something or is it really a multi step process?

submitted by /u/badassito
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