All Bitcoin Core installations to a higher and lower release I tried were upgrades on top of the old rather than complete new installs of the blockchain. I did NOT have to resort to "Add a blocksxor=0 line to bitcoin.conf file or use it as a command line arg: --blocksxor=0".
It worth noting that this is because only Bitcoin Core v28+ clients with fresh blocks directory will have XOR'd block files.
Otherwise, the block files should be the same as the previous version.
Bitcoin Core clients that upgraded from v27~v28/v29 but still experienced errors in Armory could have been caused by another issue like the one explained by goatpig above.