Assalamualaikum, Last year I went on vacation for 9 days. I know the ruling for joining/shortening is 4 days or less. Excluding the day of arrival and departure we are left with 7. Still due to some false info I thought if we change hotels it counts as new trip. Do I have to repeat those prayers?

Ustadh AbdulAziz al-Haqqan

The correct ruling is that there aren't set days for this. Even if you remain there for, let's say, 50 days, you are still excused and you can do qasr. This is the saying of Shaykhul Islam Ibn Taymiyyah as well as Al-Imam Ibn Uthaymeen, and it is the correct saying, Inshallah.