Meanwhile found a thread that adresses (and answers) the question:
https://forum.openwrt.org/t/wi-fi-channel-auto-selection/47776
[note:
option channels '100 104 ...' did worked for me
option chanlist '100 104 ...' did not
Luci does not remove the additional line in /etc/config/wireless 
but there is no way to add or modify with luci
hw: TP-Link CPE510 v3.20
fw:OpenWrt SNAPSHOT r14551-e147b9d616 / LuCI Master git-20.305.72436-6e4e132]