Jetson AGX Xavier Developer Kit PCIe x 16 slot, internal signal is PCIe x 8, in datasheet PCIe x8 lane controller, can supports x8, x4, x2, x1 links, so now put PCIe x4 card, need or not change device tree, meet target PCIe card. or auto change lanes support.
No need to change device tree.
x8 port is able to support a x4 card.