Create a new folder on your desktop called "day"
Select Alb Unpacker.
A window will appear. Navigate it to the stadium you wish to alter. Suppose you're trying to create a new version of Shea. In that case, you'd click through these choices: C:/ Program Files/ 3DO/ High Heat major League Baseball 2002/ ART2K2/ Stadiums/ Shea
Here you'll see two choices: hwdShea.alb and hwnShea.alb. Double-click the first one (the "d" in its name stands for "day"; the "n" in the other file's name stands for "night").
Extract this .alb file into the folder called "day" that you created on your desktop.
Open your "day" folder. You'll see five .mod files. Ignore them.
You'll also see five folders with the same names as the five .mod files you're ignoring. Open one of these folders.
Inside you'll see .bmp files. These are the files you can alter.
Launch the graphics program of your choice (eg. Photoshop, Paint Shop Pro, etc.) and use it to open the .bmp files and alter them.
Save your work as 8-bit uncompressed .bmp files, over-writing the old ones and using the same file names.
When you're done altering files, go back to HHEdit and launch the Mod Repacker.
Click the top button and navigate to one of the five .mod files tha we've been ignoring up until now.
Click the middle button and navigate to the folder where your altered files reside. Remember, they're on your desktop in a folder called "day". Specifically, click that folder which has the same name as the .mod file you selected in the previous step.
Click the bottom button and navigate to the same .mod file you selected two steps ago.
Repeat for all five .mod file/folder combinations (assuming you made alterations to files in each of the five folders. If not, then you need not re-pack a .mod file whose corresponding folder you left untouched).
Go back to HHEdit and launch the Alb Repacker.
Click the top button and navigate to the .alb file you originally unpacked. Remember, it's located at the following location: C:/ Program Files/ 3DO/ High Heat Major League Baseball 2002/ Art2K2/ Stadiums/ Shea.
Click the middle button and navigate to the folder that holds your recently re-packed .mod files. Remember, they reside in a folder on your desktop called "day".
Click the bottom button and navigate to the same .alb file as the one two steps above (remember that in both cases you're going to the .alb file that begins with "hwd", NOT "hwn").
Click OK as necessary.
You're done with the day version of your stadium.
Create a new folder on your desktop called "night".
Repeat all steps above, but remember to un-pack the .alb file that begins with the letters "hwn" and to then re-pack this same file when you're done.