Depends on the exact requirements. For example, rsync has --exclude and --include options. Various other copy programs (tcp, cp, ...) have similar or fewer options. But that requires cooperation from the user performing the copies. You say "do not want to let", which sounds to me like the administrator wants to prevent users from doing certain things; I do not know how to do that.
Theoretically, you could make a restricted account (perhaps in a jail?), and that account doesn't have a normal shell and can't use normal system commands like cp or rsync. This would be an enormous amount of work. It would also not work well, unless you also turn off normal shell access, because it is always possible to copy files with tricks like "cat file.1 > foobar.iso". Even more theoretically you could modify the file system code (perhaps using a fuse file system) so certain file names can't be used at all. There are commercial file systems where this would be easy to implement, using policy-based storage placement: you could set a rule that says "if a new file is named *.iso, then store it in a part of the file system that has no free space at all". But I don't think file systems with policy-based placement are available for FreeBSD (they exist as commercial products, for various Unix and Linux flavors, and for Windows).
You also need to be aware that Unix really doesn't have a "file type". The fact that *.iso files contain ISO images (of CDs or DVDs typically) is just a convention. There is nothing that prevents me from putting an ISO image into a file called foo.bar or important_tax_memo.docx.
Finally, there is no need to write in bold face ... we'll happily read normal text too.