For BBW 5.75 this is what I do to create a stadium backdrop:

Go to C:\Users\Public\Documents\APBA Games\Baseball\BallParks

You will find FL-XXXX.INI the ini file for the ballpark

F-XXXX.DIB which is the ballpark picture in a bitmap format

 

Go to C:\Users\Public\Documents\APBA Games\Baseball\Field Effects

APBA

You will find fe-xxxx.ini which is the field effect file

 

For the Stadium picture:

Find a stadium .jpg picture you like and use a photo converter 
like ashampoo photo converter 2 and convert to BMP, rename the 
BMP to DIB, rename the picture to F-DABCD.DIB for day time picture 
and F-NABCD.DIB for night.

For the .INI file:

Copy one of the .INI files (FL-XXXX.INI) as say FL-DABCD.INI open 
the file change the stadium name and anything else that need to be 
changed.

For the effects file:

Copy a ballpark with similar characteristics FE-XXXX.INI as 
FE-ABCD.INI and change some of the obvious item.

Just remember keep all 3 (4) files name the same except for 
the prefix and suffix. For Miami you could do FL-DFLOM.INI, 
F-HDFLOM.DIB and FE-FLOM.ini . The program looks for and 
matches the FLOM. Naming conventions F-HD high def. day, 
F-HN high def. night, F-LD low def. day, F-LN low def. night, 
for dome stadiums you can replace D or N with O for open or 
C for closed

Next open bbw 5.75 using the new ballpark, start playing the 
game as the home team, use any manager for the visitors. And 
load the bases with intentional walks. You will have to rearrange 
all of the players, manager and play count boxes, because they are 
scattered all over the place. Hold down CTRL and click and drag the 
object you wish to move (I always forget the Ctrl key). You will need 
to relocate 18 item, 9 defensives players, 4 offensive players, 
2 managers, 2 statistics boxes the scoreboard and the control panel. 
When you are done go to options save ballpark layout and your new 
field is ready for a game.