winmerge helps alot.
if you are doing a mod first compare the standard warlords to the mods file, then after you know the differences there go from warlord mod to bts. but it still takes some trial and error like my barbarian mod required
also note for units - i havent done it yet but i think i'll have to copy the names and classes to match in the bts file before trying winmerge. winmerge tends to skip entries until they match.
by the way what are you doing this for?