Changing First extent size by updating systables

We are trying to change the size of the first extent on many of our tables. I know we can unload the tables, and reload them; however, the amount of downtime we are allowed is much less than required to do that. One of the people I work with found that if we update fextsize in systables and alter index to cluster that the new size tkes effect. I have talked with informix, and what they say (basically) is that it is not supported, but they have no documented cases of problems being caused by this. It seems that many people are doing this exact same thing. So what I am looking for are peoples experience with this, what problems they have run across, and what benifits they have gained. What we currently do is set the next size to be large enough to hold the entire table, then alter to cluster, then set next size back to a modest growth factor. this should at best give us 2 extents per table. Thanks in advance for your help, Tony G. Peterman Software Consultant