Microsoft Office 2010 and 2013 need to be activated after 30 days. They can be rearmed 5 times, every rearm gives you additionally 30 days to activate / evaluate the product.
If you always rearm Office on the last day before it has to be activated that makes a total evaluation time of 6 x 30 = 180 days.
Although the rearm feature was made for corporate users, it cannot be illegal to use it since it is an official feature Microsoft implemented.
You can use this tool to rearm Office 2010 5 times. Just re-apply before the 30 days trial expires.