I wouldn't try and reveg an entire plant but if you want to take clones I would say it depends how far into flowering it is. Most of my killer clones came from mothers that were in flower a couple of weeks. They do take an extra week or two to get back into veg mode but its no problem usually.

On the other hand, I broke a small branch off a Mango that was several weeks into flower and I decided to clone it since I love the strain and it's only available as clone...it rooted ok after a rough start but now it's new growth is budlike, very tight with small leaves and uncharacteristic of a normal clone. Here's a couple of pics of it. It's reveg is going very slowly, (its a month old from when it got clipped and took two weeks just till it could stand on its on) I think it will eventually be normal again. (crossed fingers)

So I guess the bottom line is, it's okay to clone from flowering mothers but only a week or two into flowering...after that its a lot more difficult, at least based on my very limited experience.