Every Viceroy will also be a Member of the Parliament of Spain-Mexico. The King will now become the President. The Prince will become Vice President. Here are the current parties:

Conservative Party: 70% of Parliament Seats
People's Party of Mexico: 20% of Parliament Seats
Democratic Party: 5% of Parliament Seats
Whig Party: 5% of Parliament Seats

If you want to found a party please comment below! Also please comment if youd like to run the Democratic Party or Whig Party.