No it is fine to switch back to regular oil.
Yes you can. Contrary to a popular belief it does not hurt to switch between or mix synthetic and conventional oils.
I use synthetic oil in my 2002 PT Cruiser, and it runs great! Synthetic costs a little more, but it actually better for your engine.
Mixing synthetic oil with regular (conventional) oil generally won't harm an engine, as both types are compatible. However, it can dilute the benefits of synthetic oil, such as improved lubrication and performance. Over time, this mixture may lead to reduced engine protection and efficiency. It's best to stick with one type of oil for optimal performance and protection.
No. It won't hurt your truck...
The question is somewhat unclear, but if you're asking if it's okay to mix synthetic-blend motor oil with full-synthetic motor oil, then the answer is yes. However, it somewhat defeats the purpose of paying extra for full-synthetic oil. Full-synthetic oils lubricate better than conventional and blended oils, and are more resistant to breakdown. This doesn't mean you should go longer between oil changes, though. No matter how good the oil lubricates, it still gets contaminated with particles from the combustion process and needs to be changed. The advantage is that over a long period of time, full-synthetic oil's better lubrication will protect the interior of the engine from heat and friction better than conventional or even synthetic-blend oils. With all conditions being equal, the engine treated with full-synthetic oil will retain its original performance and efficiency longer than the same engine treated with the alternatives. How much? That's a WHOLE different question! Synthetic-blend oils take advantage of the superior lubricating properties of full-synthetic, but at a lower cost by blending full-synthetic oil with conventional oil. It is a slight improvement, but generally won't make a considerable difference in the life of your engine if you maintain it properly and change your oil regularly. Again, contaminants are the biggest culprits in engine deterioration, not cheap oil (usually, there are exceptions). Mixing synthetic-blend oil with full-synthetic won't hurt anything at all except for slightly downgrading the superior lubrication properties of the full-synthetic oil. Mixing in conventional oil is also acceptable, effectively producing a synthetic-blend oil. Just be sure to use the proper oil type as called for in the owner's manual.
You can use Synthetic oil at any time. You can even mix it with regular oil. Just be sure and use the correct weight.
Regular oil is recommended by Jeep. Edit: Correct, Jeep does not make a recomendation to use synthetic oil. However synthetic oil will not hurt the engine at all. The recommended weight is 5w30.
A good grade synthetic oil can be used in a 97 Yamaha XT350. 10-40 should be used instead of 20-50 as the thicker oil does not pump up well cold.
It won't hurt the engine but it will hurt the catalytic converter.
rapidly changing gears in anything will hurt the vechicle but not slowing down will not
It does not hurt an engine to run it with no exhaust muffler
There is not any official data as to how many people get hurt each year changing a tire. Many people may not get hurt enough to seek medical attention.