It's not that drastic :-) I do this all the time - I often add features to a beta version of mIRC that I think might be useful but after testing or feedback I may decide that they do not quite do what I thought they would do, so I remove them.
Based on the above feedback it looks like this feature has a number of issues and if I did make it optional many users would probably turn it off.
Since it was mainly added to help new users logon more easily, I would rather remove it and add a better method to help new users logon.
One way of handling this would be a dropdown, 'append 0-9', 'append _', 'do nothing', and make one of 'em default for new installs, leaving 'do nothing' as the default for upgrades that haven't yet picked an option.
