finally burned!
As I was not sure about kernel partition resize I do a sysupgrade from command line (Increasing mamba and venom kernel partition to 6MB - #113 by bmork):
sysupgrade -F squashfs-factory.img
Two times, to do the change from both boot partitions.
AFIK, henceforth, I could update from web UI with sysupgrade.bin because my kernel partition has been resized already.
Now I have to do new custom firmware to erase some redundant packages and load some forgotten packages.
Thank yo very much @Eliminater74 for your work!! Your action script is funny and easy