I'm having to reinstall LibreElec & TVHeadend on an RPi3 (TVHeadend went weird and decided not to end recordings) - no problem. I decided that to make life easier for myself I'd create a clone of the Micro SD card so if it happened again it would be a simple swap. I'm using 64GB Micro SD cards because recordings get stored on there as well (I had a lot of problems when I tried to use an SSD in a USB slot).
Long story shortened: I ended up thinking to use a live Clonezilla USB stick in my laptop running Linux Mint. This laptop has 64GB disk so I have 3 64GB disks and a 32GB disk to choose from. How, with the cryptic identification Clonezilla gives each how can I select the source & target from the three possibles (I can thankfully eliminate the 32GB memory stick).