I just figured this out, but I believe it takes up unnecessary space in your addon folder. Is the common.lvl just the load screen and it's .req?
Either way this is how ya do it.
NOTE- This tutorial assumes that you know that your loadscreen must be .tga format, 256 x 256, or 512x 512, and saved with RLE compression off. Also *** stands for your 3 letter world name
1) Open up the lua for the mode/era you want to have a different load screen for (ex. ***c_con.lua)
2) Scroll down to NOTE: There will only be a dc: there if you already have a custom loadscreen for that mode/era
3) Change it to something like this Now make sure that your loadscreen is in BF2_Modtools/Data_***/Load
(You must create a load folder if it is not there)
4) Make your loadscreen's .req Just copy and paste this into a new text document and save it as common.req
Make sure you loadscreen's .tga is called loadscreen
5) Open VisualMunge and check the Load box
Munge
6) Go to Data_***/_lvl_pc/Load
7) Rename common .lvl to what you put in your lua before (in our case it will be common2.lvl)
Note: you may want to copy common.lvl somewhere lese and then rename it
8.) Copy common2.lvl to Program Files/LucasArts/Star Wars Battlefront 2/GameData/addon/***/Data/_lvl_pc/Load (once again create the folder if it does not exist)
9) Test your map

WHY THIS WORKS
Your .lua calls whatever .lvl you tell it to and looks in the .req, finds loadscreen, and loads it. As long as each of your common.lvls have new names you can have a different loadscreen for each mode
Credits-
[RHD]Zerted- How to video for adding custom loadscreens
you can get it here

No, a custom common.lvl isn't necessarily just a loadscreen and its .req. The "common.req" you're munging for loadscreens, however, is. Like you said it's irrelevant, but you do have to munge twice, because both your .req files (whatever they're called) must call for a file called "loadscreen".

...So you munge once with firstloadscreen.req calling for a "loadscreen" (.tga), copy and past your new firstloadscreen.lvl into your "Load" folder, and then you rename the old one (or delete it) and munge with your secondloadscreen.req calling for a new file also named "loadscreen" (.tga). Copy and paste secondloadscreen.req into your "Load" folder.

I'm assuming that the normal loadscreen .lvls (which you'll notice are also not called "common.lvl," reinforcing that you can call them whatever you want) have some way of loading multiple .tgas with the same .req, and that there's some sort of naming convention that the game's "common.lvl" reads so that it knows to rotate the loadscreens. Unfortunately I don't know the naming convention otherwise it would be possible to set up changing loadscreens a la the stock maps. I know that there was some sort of game source that Teancum used to change this, but it's been since lost and I don't have a lot of information.

But yes, in summary, it's really easy to set up different loadscreens (as long as they're single screens) - it's what I did for Aquilaris and the Conversion Pack. The only catch is that each loadscreen .lvl file will add 1MB to your mapsize.

Ah ok, thanks Mav.
Also the point to this tutorial is to have a different loadscreen for each mode/era
like say you make a Hero Assault loadscreen. You don't want that coming up with the Conquest
So I think you do need individual .lvls (correct me if I'm wrong)
oh and thanks for the response, very clever