I am running Heimdal 0.7.1, and I am having some trouble using the kadmin's principal modification mechanisms when it pertains to password expiration dates.
The parser the splits the built in commands in kadmin do not (yet) support quoting,
it must be added to be able to use it in the prompt mode. You can use it in the command line mode, ie $ kadmin add --pw-expiration="2006-12-23 13:00:00" principal as a workaround for now. Love