For both PureFTPd and ProFTPd, there should be an easy way within the panel to open the ports for Passive mode and to uncomment out the setting. Same thing for enabling Active mode.
Add Ability to configure passive FTP ports through WHM
As a server administrator, I would like to be able to set up passive ports through WHM.
According to cPanel documentation, there are two steps necessary to configure this via shell: changing the FTP servers configuration file and setting the internal cPanel variable.
The instructions are good, and with a little thinking one can determine how to update the files as well, but it would be nice to have this configurable in the WHM interface. This will be especially true once FTP configuration can be pushed out using Server Configuration Clustering. :)