Yes you can defoliate and then flip to flower.
You can defoliate at any time.
Just remember you can take more off but you can put more back.
I defolate here and there throughout the grow cycle.
Why defoliate?
What for?
Are there any benefits to be had?
Why do it "just because"?
Remember...............less leaves = less energy being made = less growth.
It is that simple!
You will not get more or bigger buds from defoliation, only less.
I would not defol at all and just let them ride out you can let them try and recover for a few days and soon as they look good flip to flower after 21 days you can defol some