I asked myself if it would be possible to get the amount of usable ghosts in every level always set to maximum (which would be 8). Unfortunately I have not much of a clue about making mods, hacking or modificating hex codes. Maybe just text editing files but you get the idea.
Since this forum is still surprisingly active and I haven't found a mod which can do just that I wanted to float the suggestion somehow.
I think it's a great idea because some levels of the game are very big and also crowded like the Deadfellas one. It would be much fun to use a whole lot of ghosts there instead of just 3 to 4.