changing cabin air filter that wasn't maked to be changed on 2005 Dodge Caravan

have grand caravan & tried to change cabin air filter but only "select models" are changeable...can I cut bottom of unit and retro-fit a filter. car is in Fl. and smells like an old frig.

Asked by for the 2005 Dodge Caravan
Replacing the filter will not get rid of that smell, which is in the A/C unit.