This is normally not possible.
However I did it in the past by updating the 'owner' column
for these tables in 'systables'.
This has to be done as user 'informix', because only user
'informix' is allowed to change the systables.
There is no guarantee that this will work, so I would recommend
that you take a Level-0-Backup beforing doing this.
Also you might re-start your databaseserver after the update
because the data-dictionary-cache will not be up to date.
It is your own risk and you will probably get no support
from IFMX if it doesn't work !!