Set toggle rate in Quartus II
In the main menu (File|Edit|etc.) choose Assignments-&gt;Assignment Editor (or simply Ctrl+Shift+A).

A window/tab with the assignments will open.  In there you can add the assignment that you want, which in this case is I/O Maximum Toggle Rate for the related pin.  

The drop-down list under Assignment Name is long and alphabetically ordered, and since the option you are looking for starts with I instead of the more logical T, it is easy to miss.