The steps for running multiple copies of 4D Server on a single machine on OSX are the same as on OS 9 with one exception. Under OS 9.x, the modified tcp.opt file would simply be placed at the same level as the 4D server application. This still holds true for Mac OSX; however, under OSX, because of the concept of package contents, the modified tcp.opt file would need to be placed in the "MacOS" folder.
Here are the specific steps:
While pressing the Control key, click on the 4D Server icon and select Show package contents from the contextual menu that is displayed. Once the 4D 6.7.5 window opens, double-click and open the "contents" folder. Inside the "contents" folder, open the "MacOS" folder and then place the modified tcp.opt inside it.