No. On the Rebel T6i, the preset scene modes are fixed presets and can’t be reprogrammed to default to flash off. They’re designed to make those decisions automatically.

If you want the camera to remember your settings, switch to one of the creative exposure modes such as P, Av, Tv, or M. In those modes, the camera will generally retain the last-used settings, and flash control is more direct.

If you specifically want custom saved shooting setups, that feature is typically found on higher-end Canon bodies with custom modes, not on the T6i.

One community reply mentioned physically holding down the hot-shoe switch to prevent the pop-up flash, but that’s a workaround rather than a proper camera setting and is not the recommended solution. The practical answer is to stop using the scene presets and use P or Av instead if you want flash-off behavior to stick.