Question
Can we restrict the file types which can be uploaded to an account so it can only accept certain file types?
Answer
It is possible to limit the files uploaded to the server to be for only matching The change would need to be done by altering the FTP configuration file, so you may want to look at the following article as well on how to update the configuration properly:
How can I make changes to my FTP configuration without cPanel overwriting my changes?
The information discusses here should only be performed by a qualified system administrator. The items mention here are not items that the cPanel Support Team can perform.
ProFTPD does allow for uploads to be limited by file type. You can find more information in their documentation:
http://www.proftpd.org/docs/howto/Filters.html