Yes, they even sell it that way.
Yes, you can. It is even sold as a Synthetic Blend.
Yes.
It might be... It's highly not recommended to mix regular and synthetic oils.
Yes
Yes, you can even mix them.
Nothing happens, they just mix. You can buy "blended" motor oil.
Oil changes are always necessary. If you mean can you mix conventional oil and synthetic, the answer is yes you can.
Yes, you can even mix synthetic with conventional oil.
That's okay.
use it, it is ok to mix
Yes, you can even mix them.
No, you can even mix synthetic with conventional oil. It will do no harm at all.