Bro I am slightly aware of all the mechanics involved, but not as specialist as you:),
I am against changing the rings only without considering the pistons & other related stuff involved in smooth & trouble free running of an engine,,
I have seen when people goto the mechanics & complain about smoke, the mechanics(Usually inexperienced) only emphasis on changing rings without checking its real cause & people consider it to be a cheap solution, after doing this job 90% of people claimed that the problem arised again & cursing the car etc etc,
In the above case, I can not say anything without inspecting that what is the real cause of it, may be it some silencer carbon, etc etc, Engine oil is also a major factor of this problem,
Once upon a time, I purchased a Shell 3L can, I changed the oil of my car with it, before that my car was fit & maintained by company, just in a weak, my car start giving smoke, that is increasing day by day to dark blue or even black smoke , & my car's engine ceased, cause was Fake oil, its inspected by Shell mobile lab, & report said that the oil contains a no. of false additives