I'd also like to know if there's a way I can create a building that acts as a unit during assaults on the city, and affects the behaviour of units besides itself, as well as the unit itself starting/staying only one tile in front of the rest of the units(I want to change the way Walls work, okay?).
Um... no. That would require a heavy-duty rebuild of most of the combat engine.
Ways to have magic/buffs that cancel each other out passively, or units that get big buffs against certain other kinds of units...
Buffs can overwrite other buffs - look at Dispelled. As for getting bonuses against certain other units, that's not doable, but you can give them debuffs that only work against certain units. The anti-undead abilities (which I don't think have ever been relevant in any game of this) work like this.
knowing what all the specials do exactly would be nice as well(what does Charge and Chargebreak actually do?)).
Charge and Chargebreak are among the more complex abilities. Here's the rundown: Normally, a unit can move or attack on its turn, not both. Units with Charge are an exception - if they advance into range, they'll make an immediate attack. What's more, if the Charge value is above 0, they'll get a bonus on that attack. However, if the defending unit has Chargebreak, they'll get an immediate counterattack, which can also have an attack bonus.
I think I can see how to make new buffs, but what are buff modifiers? I remember Vanigo mentioning them when he was talking about the order in which things resolve.
Most buffs have buff modifiers, which are just flat bonuses or penalties they apply to the affected unit's stats. A few, like Improved Health, have buff multipliers, which as the name implies give a percentage-based modifier to the affected stat.
Oh yes, and I'll probably implement flooding or something. Rivers become ocean tiles, the lands next to them become rivered Swamp tiles, takes some shit to undo but can also result in good things happening...I dunno. Big overhaul, probably, in a lot of ways, how I can.
That sounds like it's best handled by the admin, changing tiles manually between turns.