I transferred ownership of some of my 529 to my youngest daughter when her older sibling started receiving financial aid. I did this even though I realized there was some risks - 1) Youngest child, as owner, can just withdraw the money (even though this was a risk, I wasn’t concerned about this one). 2) May impact youngest child financial aid if she went to a Profile school that counted it as child asset.
I figured the guaranteed positive impact on financial aid on the older sibling was worth more to me than the possible impact on the youngest child. As it turned out, the youngest child is starting a state school this year and will not be receiving any financial aid. So, in my case it worked out.