Hi Nikki,
Good news! You can visit another park earlier in the day with your Magic Your Way park ticket, then visit
Mickey's Not-So-Scary Halloween Party with your separate party ticket. Since the party has a separate ticket, it does not count as "park hopping." As of this year, you can also enter the party as early as 4 PM with your party ticket.
On party days, we have visited other parks, but sometimes we have taken a day to rest and play at our resort. The kids love having some dedicated pool time and we all feel energetic for a late night at the party!
Thanks for stopping by the Disney Parks Moms Panel. As you continue to plan your trip, let us know if you have any other questions!
wishing you happy planning and a magical vacation,
Amy H