This is what I've done so far, I cloned the inflatable pumpkin and added a pie menu string that says 'go trick or treating' I then got the BHAV for 'go hiking' so that sims can disappear off the lot and then come back and I can pretend they went trick or treating, I even added a memory of 'went trick or treating' however as you'd expect, the text bubbles that pop up when a sim comes back are the same as when a sim goes hiking, I don't know how to go about changing that. I did extract the dialogue text for 'go hiking' and it's sitting in a folder because I'm not sure what to do.

It's okay, I've sorted it now. I used the jogging mod by smonaff instead of hiking and it works much better, I took out the warm up animations and the change into actives clothes. I also added a memory of trick or treating and managed to make cookies appear in their inventory. It still has a few issues that need sorting though but I'm happy.