In flower can I stop it.

So I went to long before changing over to 12/12 and now to big for its area. I have a bigger tent on the way. Can I reveg the plant to make it bigger currently its two foot tall and just started to flower. And that is with lst.

you can, the longer the plant has been under 12/12 the longer it will take to go back to veg and visa versa.
I'd just grow it out in the bigger tent and make notes for the next grow. You might find they keep stretching in the new tent. At least you'll have some decent buds to smoke while your next crop is going.
Also you could use the smaller tent for germination and the first few weeks of vege, shave a few weeks off your cycle.
just something to think about.