This information is from the Secretary of State's website:
A write-in candidate for U.S. President, U.S. Senator or U.S. Representative must file a written request for his or her votes to be counted. This request must be filed with the Office of the Secretary of State no later than November 1, 2016.
Presidential candidates must also include the name of a vice-presidential candidate and the name of at least one, but not more than ten, candidates for presidential elector.
We received further clarification from the Secretary of State's Office:
When you vote for a write in candidate, you will fill in the oval/square next to the write in candidate space on the ballot. That “write-in” candidate spot will receive a number as to how many people filled in that oval/square. So, the “write-in” candidate for that office will receive a number on election night. That vote is counted and is a part of the official report from that precinct. The names that are written in that spot will also receive a number associated with the name, if that name is a registered write in. That is a separate report completed by the election judges/absentee ballot board members.
You can click here to see all the candidates for office for President/Vice President on the Minnesota ballot.
The list of individuals registered as write-ins will be continuously updated until November 1. You can contact the Secretary of State's Office for an updated list.