Hello,
If you only interrupt the router while booting IOS and change the configuration register to the 0x2142 then the original configuration will be left intact. It will not be affected.
Pay great attention to not to store any configuration using the commands copy running-config startup-config or write memory. That would overwrite the stored configuration with the current running-config which may well be a simple empty configuration. Even if you change the configuration register back to the value 0x2102 in the configuration mode, do not store anything. The configuration register change is applied immediately and it does not require storing your running configuration anywhere.
Simply, do not save any configuration changes and you should be safe.
Best regards,
Peter
