I think. I have not tried.
It has to be stripped of the header of the original firmware with hex editor up to the sequence in hex 01 00 00 00 54 50 2D 4C 49 4E 4B (cut the first 0xE684 bytes) and flash with the mtd method.
*Original Firmware
https://static.tp-link.com/2018/201802/20180209/TL-WA850RE(US)_V2_171228.zip
*Firmware stripped
https://www94.zippyshare.com/v/C7RB6EoI/file.html
md5: adfedabce6ea3ff732e3cd99bbe0835b
sha1: 1044b37ab4fe5f0895794ab436ee4f54d196f167
*mtd method
mtd -r write /tmp/firm.bin firmware
*serial method
tftpboot 0x80060000 firm.bin
erase 0x9f020000 +0x3812E6
cp.b 0x80060000 0x9f020000 0x3812E6
bootm 0x9f020000
NOTE: I think. I have not tried.
@SantiagoAcevedo @leomanias