In addition, if you don't want your users accidentally (or deliberately) messing with their mailfile design, you can run the Desgin task in a Program document on the server - say, each night.
I have a set of users who are consistently getting excellent mileage out of their Manager access to their mailfiles (which they need for a pilot they're on) so I actually run the Convert task nightly. This tool seems to be better for my purposes as some of these users simply choose new designs rather than editing their own.
Either Domino task should cut down on your support incidents for design problems, though

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(Beware: if you use the Convert task on a 6.5.x server, check for a spelling/syntax error in the exe at compile time, meaning some of the arguements need to be given without spaces, as follows
load convert -g"English" -u -r mail\*.nsf * <<newtemplate'sfilename>>
The language stipulation is necessary due to another bug I can't remember, which also causes the problem you raised this post about!)
Cheers...