Major rearranging, moving shelving around as well as toys, feeders, and stuff, I try to do a couple times a year. Toys and perches like the lava ledges get rearranged once or twice a month, or when I get something new or refill a toy.
It really depends on your chins though, some love change, and you can redo the whole cage to look brand new. Others it stresses them out and you need to change things out slowly, maybe only one thing at a time over the course of weeks. So you need to know your own chins and what their personal comfort level is. Also when doing a major rearrange be careful if your chin is one that likes to run full speed around the cage, changing where ledges and perches are can cause a fall if your chin isn't careful.