One correction... this is not a "request", it is a demand. They will be loading new firmware that does not allow 10/8 internal addressing. If you are still using 10/8 internally when the new firmware is loaded, your network may cease to function. If your network is all DHCP and you have no pinholes, you won't notice a thing. If you have any static (or reserved DHCP) assignments, those machines will no longer have connectivity. Any NAT pinholes referencing a 10/8 address will be invalid, and thus deleted.
I have seen at least one thread from someone with such a router, and it will error out when you try to use a "10." address.