Is it possible to force custom DNS addresses via LEDE on TP-Link TL-WA701ND where TP-Link would be connected via cable to my ISP router, with disabled Wi-Fi, and transmitting Wi-Fi?
ISP Router / Wi-Fi disabled -> lan --> TP-Link LEDE / Wi-Fi enabled-> force DNS on all connected devices
adblock package creates the following rule that should match your requirement - edit /etc/config/firewall and add:
config redirect 'adblock_dns'
option name 'Adblock DNS'
option src 'lan'
option proto 'tcp udp'
option src_dport '53'
option dest_port '53'
option target 'DNAT'