The i.MX6 series reference boards by Freescale have the switches to select the available boot media, including an SD cards. For the i.MX6DualLite SABRE SD board, this is SW6, for the i.MX6DualLite SABRE AI board, these are S1 and S2, please check the corresponding hardware schematics. So, you don't have to modify the hardware to choose the desired boot media.
Have a great day,
Artur
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