Yes, you can prevent your CC computers to boot from disks.
But you have to change code within the ROM folder, i.e. you can only change it from outside of Minecraft!
If you're picky about it being ROM (you know, read only and all), then you could look at it like a computer company just producing another series of computers, with a new ROM. />
How do I disable booting from disks?
Can I limit booting from disk to specific computers only?
For example, if you didn't outright wanted to disable the possibility of booting from disks altogether, but still wanted to limit it, you could rename the "startup" for the disks, to something else that nobody but your "Maintenance-Team" on your server knows about.
It'd then act as some kind of password. But of course only as long as nobody finds out about it by finding a disk with a weird file name on it. />
So this way it isn't secure per se (security through obscurity never is), but it prevents people booting from disks, who only know about the default "startup" file for disks.
But why stop here?
You could just as well insert code that forces users to enter a password if they want to boot from disks.
It's limited pretty much by your own ideas and programming skills.
But please don't go wild and publish dozens of new hardened, secure "OS"s.
Let people do that by themselves and learn something in the process.
(Not that these would be OSs to begin with. If anything you've created a modified shell.)
K, hope this was interesting enough for some, take care! />