I change my guys cage in phases, mostly because I have a lot of ledges and perches to move around and it requires me and my husband to change around the things on the sides and back of the cage. Also as said it can also depend on the chin, mine love having things rearranged they run around their cage like people checking out a new home, lol, chattering to each other and exploring everywhere. Other chins act like they just got a new cage in a negative way and will hide and need time to adjust if you change things too fast. Some chins also like to zoom around the cage, and when you change the location of landing spots they might fall (forgetting a ledge is no longer there) until they get a new route figured out, so all at once might be better so nothing is the same. So long as you are keeping the old items though it's normally not too stressful since their scent is still on everything, but it comes down to the personality of your chins, are they shy and skittish? or more outgoing and brave? or something in between.