If you want to use u-boot from OpenWrt, you can upgrade it safely.
* bl2: openwrt-mediatek-filogic-glinet_gl-mt6000-preloader.bin
* fip: openwrt-mediatek-filogic-glinet_gl-mt6000-bl31-uboot.fip
`openwrt-mediatek-filogic-glinet_gl-mt6000-squashfs-factory.bin` is used in OpenWrt's u-boot.