pro.apply @ 21.06.17, 13:29
TWRP on my machine put together a custom kernel.
No, do not put it on your machine, together with a custom kernel. It is perfectly placed separately.
pro.apply @ 21.06.17, 13:29
And for Magisk v12.0 rekaveri need stock.
Who told you that? Magisk-in anyway, that there is a rekaveri you should.
pro.apply @ 21.06.17, 13:29
The question itself - how to put Magisk without root in the stock bootloader?
Sews TWRP (temporary or download it if it is on a regular basis you will not need it) - it sews the latest beta version of Magisk.
Everything.
Read more in the profile subject of your device.