I was mixing a song las week. To set it up I’d drag the audio files to the arrange windows mapping each audio file to an audio track using the Track>Create command from the Arrange window to add more tracks to the arrange window as I needed them. When I reached 72 tracks Track>Create wouldn’t add any more. So I went to the Preferences>Audio tab and set the parameter Max. Number of Audiotracks from the default 72 to 120. Then went back to the arrange window and tried Track>Create, didn’t work. After a few unsuccessful attempts, some environment editing, a good look at the Logic manual and some head scratching I couldn’t find what was I doing wrong so gave up for the day, saved the project and closed Logic. 

I tried again the next day. However, that time I was able to add all the tracks I needed. This is how I found out that the parameter Max. Number of Audiotracks can be modified at any time but is only taken into effect after restarting Logic.