As far as how, the difficulty depends on what mod you are trying to do. The basic tool you'll need is a debugger like the one in pSX. To use a debugger, you need to learn the basic MIPS CPU codes and it would help to have a general idea of how games use those codes to accomplish data processing.
Attached is a beginners tutorial I made for someone here a while back. It takes you through a fair amount of the basics.
For duredure's A, you need to find the routine that gives EXP for winning a battle. Right before the EXP is granted, inject an 'intercept' that runs extra code. The extra code would check the year, and adjust the extra EXP accordingly before jumping back to the regular game. The code needed for this would be quite simple.
B would be a bit more complex because you would have to be sure you weren't overwriting an existing creature, but the process is the same as A. Find a process that is only run for enemies, inject an intercept that jumps to extra code. I think creature slots are at fixed locations in RAM for each country so the extra code would just scan for a free slot and add a creature to that slot.
C requires finding a way to differentiate between player and COM controlled units. This is especially difficult because the "AUTO ACT" feature essentially turns player units into COM units. But if you did find a way to differentiate between the two, you'd just add an intercept in the EXP+ routine that doubled EXP value for COM units.
D is easy too. The mana earned by each castle is probably hard coded into the game. Just search for those values and double them. Alternatively, you might be able to inject a single extra op into the Mana+ routine that doubled the value before it was awarded (ie SLL by 2).
E should be easy also, the values are hard coded into the game and you could probably find them by just searching.
F is hard because you have to juggle textures in VRAM as well as run add routines for displaying the 3d models and the models themselves. It can be done, but probably never will be because the end benefit versus the time it takes to implement make it not worth it. If you were going to spend that much effort, you would be better off making a new Brigandine installment or continent map.
As far as mods I'd like to see in Brigandine, mostly I would enjoy a mod that reworked creatures, abilities and items to where everything was specialized and useful. I've dumped even high level mermen for a level 1 dragon. Mermen just aren't useful. But if they gained a ranged attack or a healing spell, maybe they would be?
Attached is a beginners tutorial I made for someone here a while back. It takes you through a fair amount of the basics.
For duredure's A, you need to find the routine that gives EXP for winning a battle. Right before the EXP is granted, inject an 'intercept' that runs extra code. The extra code would check the year, and adjust the extra EXP accordingly before jumping back to the regular game. The code needed for this would be quite simple.
B would be a bit more complex because you would have to be sure you weren't overwriting an existing creature, but the process is the same as A. Find a process that is only run for enemies, inject an intercept that jumps to extra code. I think creature slots are at fixed locations in RAM for each country so the extra code would just scan for a free slot and add a creature to that slot.
C requires finding a way to differentiate between player and COM controlled units. This is especially difficult because the "AUTO ACT" feature essentially turns player units into COM units. But if you did find a way to differentiate between the two, you'd just add an intercept in the EXP+ routine that doubled EXP value for COM units.
D is easy too. The mana earned by each castle is probably hard coded into the game. Just search for those values and double them. Alternatively, you might be able to inject a single extra op into the Mana+ routine that doubled the value before it was awarded (ie SLL by 2).
E should be easy also, the values are hard coded into the game and you could probably find them by just searching.
F is hard because you have to juggle textures in VRAM as well as run add routines for displaying the 3d models and the models themselves. It can be done, but probably never will be because the end benefit versus the time it takes to implement make it not worth it. If you were going to spend that much effort, you would be better off making a new Brigandine installment or continent map.
As far as mods I'd like to see in Brigandine, mostly I would enjoy a mod that reworked creatures, abilities and items to where everything was specialized and useful. I've dumped even high level mermen for a level 1 dragon. Mermen just aren't useful. But if they gained a ranged attack or a healing spell, maybe they would be?