It's a shame all the negativeness you received from your post. Yes, by default you can not chmod via ftp. But, we are after all still just using proftpd, and if proftpd has the feature, you can implement it on SME server.
I searched for proftpd and chmod and guess what, proftpd has the feature and here is a link on how to get it to work.
http://www.castaglia.org/proftpd/doc/contrib/ProFTPD-mini-HOWTO-Umask.html In short:
<Limit SITE_CHMOD>
AllowUser xxxxx
DenyAll
</Limit>
I tested this and was able to chmod files via ftp with no issues. If you do implement this, then you will have to create the appropriate custom-templates and also work to determine what, if any, security issues you may raise by implementing this feature.
But, your question is can it be done, and from my testing, yes it can. Whether you really want to enable it or not, is your issue as it's your server.
Others should rightly point out the security ramifications of doing this, as if the server gets compromised based on something you changed from the base, then you'll be pretty much on our own to to take the appropriate acton.
Good Luck,
John Bennett