Yes if it is mixed then the life of the coolant is reduced. Any Nissan dealer should know about the new coolant requirement. Nissan sent out memos to the dealers to make them aware of this.
However in my opinion no coolant is good for 10 years. Just because it doesn't freeze or boil doesn't make it good. I still change my coolant every 30,000 miles. It is inexpensive to do.
This is from
How often should I change my antifreeze? — Yahoo! Autos
Corrosion Inhibitors
The life of the antifreeze depends on it's ability to inhibit corrosion. Silicates, phosphates and/or borates are used as corrosion inhibitors to keep the solution alkaline. As long as the antifreeze remains so, corrosion is held in check and there's no need to change the coolant. But as the corrosion inhibiting chemicals are used up over time, electrolytic corrosion starts to eat away at the metal inside the engine and radiator. Aluminum is especially vulnerable to corrosion and can turn to Swiss cheese rather quickly when conditions are right. Solder bloom can also form in copper\brass radiators causing leaks and restrictions. So changing the coolant periodically as preventative maintenance is a good way to prevent costly repairs.
The basic idea is to change the coolant before the corrosion inhibitors reach dangerously low levels. Following the OEM change recommendations is usually good enough to keep corrosion in check, but it may not always be the case. That's why more frequent changes may be recommended to minimize the risk of corrosion in bimetal engines and aluminum radiators