(This is an idea I had, though I have no intent on doing it nor have the time, I just want to know if it can be done)

You know how when you complete a level of campaign, the UI receives the information about the level you finished and on what difficulty, right? Can the campaign maps send and the UI receive other variables if set to do so? Because I had an idea about a campaign where at situations you get 2 objectives and can only do one sort of thing, like help your friends or follow you orders sort-of thing, and I was wondering if what choices you had could be transferred across to the UI, then to the new map, or something. Influence the ending, and all that jazz.

And since you would need a modded UI and all that to do it, can a UI load off it a separate UI map purely for that campaign, and that 2nd UI is the one receiving the special info?

No

Open sauce could do part of that, but not all. It could handle variables being persistent in between maps.

The UI part, probably not, sorry.

First of all, the campaign maps doesn't send anything to the UI, it only overwrites the savegame of the profile as it is programed in the engine... The ui reads that savegame and you can see that data in the game..

To get your idea to work, we need to modify the engine, and i don't think it is really possible even with OS (or it will take a lot of effort and time which nobody will spend on it)

I'm_the_only_one_whose_allowed_to_be_right.hsc

Stock halo can handle passing variables between maps.

OS can call upon a widget via scripts, so have the campaign list button that will call a script that checks what variables are cleared, and call the appropriate map list dependent on your route.

Your problem comes in, that the variables being passed between maps is exactly that; being passed between maps, not saved or stored. You need to properly store the variables in the UI after they're received, then save (I haven't ever tried checkpoints in a ui.map, but if they work, then go for it. You'll most likely need to use core_save. But, that saves to a generic file.. if any other map uses core_save, then your ui tries to core_load, it will crash halo.)

I prefer Squirtle, personally.