I updated the footer message by changing MOD_FOOTER_LINE2, but that seems like the incorrect way to do it. I'm afraid it will be overwritten with updates. I can't find documentation to permanently change the footer. Current articles reference older frameworks and/or links to non-existent pages.
You can override this language constant so it will not be affected when you update.
Go to Backend >> System >> Language Overrides >> and new override for above language constant: MOD_FOOTER_LINE2
and change to your own text.