Yes its still XML, and yes 'probably' a config from 2.4.3 can be 'somewhat' imported even on 2.2.x.
HOWEVER, it wasn't tested or even intended to work, and you will certainly loose some configuration settings (assuming you use those parts that were changed.) and end up with a 'dirty' configuration some tags could be there that shouldn't be, other might be missing that are normally always there..
When going to a newer config version 'upgrade steps' https://github.com/pfsense/pfsense/blob/master/src/etc/inc/upgrade_config.inc can involve modifying existing settings into a newer 'format' restoring the new config format on a old pfSense version will likely mean those converted settings are not understood by the software and effectively 'skipped' or cause other unexpected problems..
I'm not saying its impossible, and well sometimes like in this case the config didn't change and it can be done without a possibility for trouble.. But be very careful and double-check everything is still in working order when restoring a config on a old version.
Usually a increase in version number also means some config upgrade steps where added.. so your a) and b) are done together, and yes tags get deleted/replaced or little changes to their meaning..
My 2 cents :).