Question 1 - 2013 Octavia 1.6 diesel turbo  has 225 by 45 by 17  Wheels/Tyres, which I find are rather harsh on ride comfort.  Is it feasible to fit smaller  but higher profile  tyres  without  other alterations on the same rims?

      Question 2 - What is the life expectancy of  Diesel Turbos assuming regular servicing with recommended lubricants?

yes you can, 16's give a good handling/comfort split - need to make sure the rolling radius is the same or the speedo will be out:

http://www.willtheyfit.com/

 

erm do you mean the engine or the turbo, I assume the latter ..that's very difficult to say depends on service, driving style, weather conditions my old turbo was at 189,000 before it started to go.

if you nail a turbo from cold,lots of racing starts,  then switch it straight off when its been working hard (so still full of oil) expect it to go a lot sooner. but could also be pot luck if something just happens to go wrong