I have got 1996 850 turbo.

Last time the oil change was done on 15th April... but it was not synthetic and I am not happy with it... So I have decided to suck out about quart of oil from the dip stick and add the same amount of best possible synthetic oil (maybe Mobil 1 10 w 30).

I used to do this with my old car regularly in-between the oil changes(twice)... I was told that the volvo is entirely different proposition so I want to know that : Will all this be of help to the car ( to Volvo) or is it just waste of time and money or still worse.

It won't hurt a bit, and might help a bit. Just think of it as blending your own part synthetic.

i always see oil changes without filter changes akin to taking a shower and not changing undies.

What, exactly are you trying to accomplish? Makes little sense to me. Even if you used el cheapo oil and don't want it in there consider it a flush and drain, change filter and refill with the best possible oil; Amsoil or Redline.

If you want to leave the el cheapo oil in there for a few thousand miles, do so. No harm will be done.

I would either just change all of the oil or drain a little. The dip stick will not yeild much oil. Your better off opening up the plug just enough to let some oil trickel out.