Hi, it seems that the band you changed may be changed to the default one automatically after you restart the module.
You can try to use the new firmware of RAK811 which is developed based on keil MDK and you can config it to any band the hardware supported by AT command. After you config the band, it will never be changed automatically.
You can find the source code and docs on Github and try to use it: https://github.com/RAKWireless/RAK811_LoRaNode
As i know, the CoIDE has not been supported by official.
Why you need this tool? for RAK811 source code on Github?
If it is, you can try to use the new firmware of RAK811 here: https://github.com/RAKWireless/RAK811_LoRaNode
It is also an open source project and based on keil MDK.
This two firmware isn't in common use. But the firmware for the tracker board is open source,and you can be based on this development.Use this site to download the open source of the tracker board:https://github.com/RAKWireless/RAK811_BreakBoard.
You could use Platformio and Ebiroll's repo to program rak-811 tracker board along side with stm32flasher as SWD debugger, the i2c protocol is working fine. Plus the repo has a BME280 library Apis for ease of access.
**Note include the library header <OBME280.h> in the main.c and call i2c_bme280_begin(); after MCUInit() before peripheral_init() in the int main() function before the main loop
I am not sure if its the right choice. Some things might be different and even configuring in EU band wont perform the same way. The hardware might be designed to emit at 915 MHz frequency. Check the datasheets of both to spot any difference.