There may have been changes because the firmware is constantly being worked on, which means that things within it are inevitably changing.
Unfortunately, there is no documentation available that explains every detail that has changed. Generally, the changes are documented on the firmware download page. For example, RUT950 page here. Are you experiencing difficulties in locating certain configuration files?
Please, keep in mind that RUT951 does not support legacy firmware due to the product being relatively new when compared to RUT950.
Since you were using legacy firmware, you should know that some features were removed with 07.0 firmware. You can find more information about deprecated features here.
Also, you can use UCI commands to configure the device via the command line. You can refer to the UCI command usage page here.