Morgh's text editor works in WFaS, too. This means we're able to tweak items, parties, troops etc. We can also make
new troops, but because WFaS has removed upgrading troops, they can't be acquired without coding.
Well, since Medieval Europe was done mainly with Morgh's editor and OSP stuff, I wouldn't say that module system is must. But you can't do
Blood & Steel without module system =)