how to disable/configure UART1

[HEXFFFFFFFF]

I ran into a problem. I am unable to disable or reconfigure UART1. Any changes to the file .overlay does not give effects. I paste into the file nrf9160dk_nrf9160_ns.overlay strings 
&uart1 {
status = "disabled";
tx-pin = < 0x8 >;
rx-pin = < 0x9 >;
}; 

but UART1 still working on pin < 0x00 > < 0x01 >

I also tried disabling UART1 into config CONFIG_TFM_SECURE_UART1=n but that didn't help either.

[mytzyiay]

When having trouble getting DT overlays to take effect, I've found it helpful to check the combined .dts file (build_dir/zephyr/zephyr.dts in my case) to see what the final combined result looks like.  The path to this file is shown when running e.g. `cd build ; cmake -GNinja -DBOARD=nrf52840dongle_nrf52840`

[HEXFFFFFFFF]

that's the problem. i check build_dir/zephyr/zephyr.dts and everything is right there, but it has no effect. any other changes in zephyr.dts  apply norm. 
There is an impression that the initialization of UART1 is rigidly prescribed in the code of some module. And this code overlaps zephyr.dts setting.