Unfortunately, the dpi parameter is hardwired in the <$referencename> building block used in the ImportedGraphicsLOR paratag that lists the imported graphics.
You could search for the dpi value with the wildcards option:
@ * dpi
(Space at the beginning. Whole Word deactivated! Use Wildcards activated!)
Then replace with nothing. Test it with some values and then do a global
search and replace.