I think I have this cracked for Wineskin. Please not that I am NOT an expert so there may be an easier/better way to do this.
Do step 1 above, and be sure the files are saved in 640x480 size (which I had some issues with the first time I downloaded them). You'll need to locate the Wineskin app (the one you click on to play EQ), right click and click "Show Package Contents", then drill down on your drive_c into the Everquest directory to find the Resources folder which contains the loadscreen.jpg file. Copy the three loadscreens there.
In the Package Contents top level, navigate to Contents/Resources, locate the WineskinStartupScript file and open it in an editor (I used XCode but I think any editor will do)
At the bottom, under "# ENTER COMMANDS HERE" enter the following commands:
Code:
RAN=$[RANDOM%3+1]
cp Resources/drive_c/"Program Files"/Sony/EverQuest/Resources/loadscreen$RAN.jpg Resources/drive_c/"Program Files"/Sony/EverQuest/Resources/loadscreen.jpg
Check the path in the "cp" command closely above. If your loadscreen jpgs are not located there, then you might have to adjust the path for your particular setup. The quotes around the "Program Files" are needed to handle the space in the directory name, which took me a long time to figure out!