Is it possible to stretch out a tied tongue?

Not really. Tongue tie needs to be surgically clipped. If you try to stretch it out, I guess theoretically you could tear it. But this would cause significant pain and probably bleeding. I would not recommend it.
Depends. Tie's are variable. The structure is a normal one, but usually tucked back under the tongue enough to allow normal mobility. If its attachment moves forward it restricts more and at some point only cutting the attachment will free it to work normally. I have seen some less prominent ties appear to stretch out enough to be left alone. (over years) Experience can decide which is which.