(This is my first topic, I advancely beg pardon for possible mistakes.)
After days of research I discovered that is sufficient to cut the first 64k of the stock firmware like that:
dd if=tp_recovery.bin of=tplink.bin skip=129 bs=512
I've also added the procedure on the device page
https://openwrt.org/toh/tp-link/tl-wr841nd
Cheers.