Say I have a (hypothetical) team of Tyranitar, Magnezone, Jolteon, Slowking, Keldeo, and Lugia. Their items are:
Tyranitar [Choice Scarf]
Jolteon [Air Balloon]
Keldeo [Life Orb]
Magnezone [Red Card]
Slowking [Assault Vest]
I register these bad boys for an official Nintendo tournament. Once the tournament begins, am I able to swap the items around, say moving the Choice Scarf from Tyranitar to Jolteon, or the Leftovers from Lugia to Slowking. This adds variety to the team and lets it function under many different circumstances. I know that this was allowed in 2010 (Gen IV), but is it still allowed in today's tournaments?
Read this article to see what I mean.