Hi,
I am trying to add modify/add some files inside an openwrt sysupgrade image using firmware modification kit. It seems to extract it fine, but
when I try to do ./build.firmware.sh which used 256kb blocksize for flashsquashfs, it says

ERROR: New firmware image will be larger than original image!
Building firmware images larger than the original can brick your device!
Try re-running with the -min option, or remove any unnecessary files.
REFUSING to create new firmware image.

So I try it with -min again, the image generated, does boot, but I get a lot of

[ 25.490000] jffs2: jffs2_scan_eraseblock(): Magic bitmask 0x1985 not found at 0x00a40018: 0xb0a2 instead

and get a kernel panic, unable to mount rootfs.

Is there something else I have to do to repack extracted images using FMK, or is there some other way to repack extracted rootfs?