Theoretically... if you have a (trusted) "friend" that has a full unpruned node, one can simply copy the blocks/chainstate and drop them into a new node installation and "voilà", you have your full node without having to download anything, you just have to trust your "friend".
Dont do this.
You can just do a full reindex, right? If your own Bitcoin Core installation verifies all the blocks you copied from your friend, you don't need to trust him anymore.
Usage: bitcoin-qt [command-line options]
Options:
-reindex
Rebuild chain state and block index from the blk*.dat files on disk
I expect this to take a day, so I don't want to test the command.