I've previously unbranded a W810 with new security model too. I've tried using FAR and XS++, it failed.

I've then downloaded SETOOL2lite and it worked.

I've choose W810 as phone type,

then for the files column, i've added main firmware first, then FS second. I then pressed flash.

after the flash finished, I've removed the battery, then put it back in. I've went and downloaded a Custom Pack (.zip file). also i've pressed clear for the Files Column.

i've put the .zip file (Custom Pack) into the MISC Files. then pressed flash again