24-bit parallel TFT module on circuit designed for 16-bit parallel
Many TFT modules have options to operate in a variety of modes.  In some cases, configuration is accomplished by strapping certain pins; in other cases, it is accomplished by having some configuration commands which can be issued using a subset of the pins, and which tell the module whether or not to use the rest.  You may have to check the data sheet both for a module and for the controller chip(s) that it uses to find out whether you will be able to configure it suitably (in some cases, a controller chip will allow configuration by strapping one of its pins high or low, but the module may strap that pin itself rather than exposing it to the outside world).