You want to change the DHCP IP mode of your OpenELEC system to static IP, but you can only access it via LAN at the moment for whatever reason, so you cannot do it via GUI.
(Background: You might want to open certain firewall ports only for certain static IPs, or avoid problems with DHCP routers. Especially in Austria, many A1 modems include a DHCP server which is extremely buggy, loses routes, host names etc.)
Using OpenELEC, you will not find IP settings at the usual places like /etc/network/interfaces or similar.
This is the path for a Raspberry Pi 2 system, but I am pretty sure it is similar to other devices:
Don’t get confused because of the .cache directory, the settings are saved permanently anyway.
The „xxxx“ stands for the MAC address of your device which you can find with command „ifconfig“ -> e.g. at part „eth0“.
In the „ethernet_xx_cable“ folder you might find other settings files with various endings. As far as I experienced, you can ignore them all and only make changes to the „settings“ file itself.
Example for a static IP setting:
[yourMAC] #CAUTION: Leave the original first line with your MAC in the file!
Save the file, reboot your device and you should be able to access 10.0.0.124.