I have been working on a Short Castles mod which (obviously) makes the castles shorter, to make it easier to see over the top of the castle. However, I've run into the problem of being unable to find the slp files to modify that determine the snow, flame, and flag position on the buildings. Are those actually a property of the .dat, or what files should I be looking for?

i think the snow is added automatically

the flag, the shadows, the damage fire are all composed slp's made by offsetting the primary slp's with xy offsets

Snow is same as fire: Graphics are stored in .drs as small white blots, .dat where are the position of it.

So it looks like I can't change the position of fire/snow as a visual mod, then. (you can't edit the .dat with a visual mod, right?). Pretty sure the flags are the same.

Exactly.