It can do yes you mite have to tinker but you could be fine.
Write down all your settings or take pic of the bios before in case you have to clear the cmos.
If your 8700K is rock stable then at those RAM speeds I very much doubt it will have any effect on your CPU overclock. I presume you're running at XMP?
I have never had any issue going from 2 to 4 sticks and iirc the topology of Z370/Z390 means the board prefers 4 sticks to 2.