TD4 piston ring change blue smoke

Recently bought my first TD4 (previously owned 1.8). After servicing i noticed that when you rev it to 2000rpm i got huge amounts of blue smoke. I changed the crank case breather for BMW cyclone so im sure its not the breather valve. I had overfilled with oil (tried to put 6.5 liters in without checking). So i drained the excess oil out so its now 1/2 way between the upper and lower limit on the dipstick. The amount of smoke has now reduced and is only apparent between 2000 and 3000 rpm along with a flat spot and misfiring. Once the engine is hot it stops smoking. There seems to be a very small flat spot at about 1000 rpm as well. I was hoping that the smoke was the result of the overfilling and excess oil would eventually burn off, but it hasn't. The turbo pipes are wet with oil but don't have any holes or splits. If i take the turbo out of the equation by removing the air intake pipe (so the engine is not turbo aspirated) it smokes even more (still blue/white smoke rather than black). I have read some other threads about the problem and the only cure seems to be a head overhaul. Having removed the head on my 1.8 to do the head gasket I really don't want to remove the head on the TD4. I had to replace one of the pistons on the old 1.8 and am sure i did this with the head on. Does anyone know if this can be done on the TD4. My thinking is that I can remove the pistons (replace the rings at this time as they might be the problem) and clean some of the carbon in the chamber without removing the head (it won't be the best job ever but could stop the smoking). I am hoping its not the turbo causing the problem but have read that a blown seal on the turbo can cause the symptoms with the smoke clearing at about 3000 rpm. Any thoughts