Modding on Mac is actually quite feasible now.
Booster's Lab is written in Java. It works on Mac. I tried Booster's Lab on Linux and I was able to make a simple Cave Story mod on Ubuntu.
The Java Doukutsu Assembler, the hex assembly patcher, and the Python Doukutsu Assembler also work on Macs and Linux machines, if you want to be hardcore and attempt to edit the Mac and Linux Cave Story executables (NO "real" documentation for Mac/Linux exists, except for a few Mac offsets). You will need a Macintosh hex editor, because I have no idea if there exists a Macintosh program that essentially does the same thing as OllyDbg (Windows-only debugger program).
However, tools like the Save Editor will not work on Macs, because the Mac saves are a different format (why???). The Physics Editor will not work on a Mac, because it's hard coded to modify certain values at certain offsets. Unless you write a plugin in the Mint Programming Language and insert it into the Physics Editor, which will (supposedly?) allow it to work on a Macintosh.
EDIT: You can definitely edit TSC on a Mac too. Celticminstrel and I both wrote two separate TSC translators for the Mac. Of course, I am a total moron and didn't realize that Celticminstrel already wrote the entire program before I started working on another copy. Both translators are written in the Python Programming Language. Somebody else (see the Tribute Site downloads page) also refactored my code so it runs far more efficiently than what I originally wrote.
Macs come with Python installed. If you think your Python version is too old, attempt to Google "Jython", which is Python written in Java. It just runs a JAR file on the Java Virtual Machine (aka the JVM).
Even better, Noxid has created a free and open source TSC editor for the Mac, written in Java. In other words, because it is possible to run every existing Mac modding program on top of some kind of Java installation, we would be screwed if the JVM did not exist.