SOLVED
Create .ftpaccess file in directory that needs to be read-only for account [email protected].
Content of the .ftpaccess file:
<Limit WRITE>
DenyUser [email protected]
</Limit>
That's all.
Please note:
Commands in .ftpaccess file are recursive (i.e. affects all the files in the current directory and any subdirectory).
Condition is that server supports ProFTPD.
More about ProFPTD here:
http://www.proftpd.org/docs/howto/Limit.html
Warning: ProFTPD is quite powerful. If you make a mistake and therefor you can't edit your files via FTP anymore, you can still edit .ftpaccess file via the command line.