not really
No, you can even mix synthetic with conventional oil. It will do no harm at all.
Synthetic and conventional oil can be mixed and used with no problem. That is exactly what a synthetic blend that you can buy is. A mix of synthetic oil and conventional.
Yes, you can even mix synthetic with conventional oil.
Yes, you can also mix it with conventional oil creating a blend.
Yes you can mix different brands but I recommend you do not mix different weights. You can even mix synthetic oil with conventional oil. But as the weight of the oil is critical, do not ever mix one weight of oil with another, no matter if it is synthetic or conventional oil.
Who told you it is not recommended? You can mix synthetics as long as they are of the same weight. You can even mix synthetic with conventional oil.
Yes, of course you can. You can even mix synthetic with conventional oil.
Yes, you can use synthetic, conventional, or a mix of the two.
Yes, semi synthetic is a blend of synthetic and conventional oil already.
Yes, you can even mix synthetic with conventional oil.
Yes you can. Contrary to a popular belief it does not hurt to switch between or mix synthetic and conventional oils.
Yes, or you can mix them. Just bear in mind that if you mix them, you must maintain as if it were straight conventional oil and that by mixing, you lose pretty much all of the benefits that synthetic oil has.