I was just wondering …I am using the render selection to sample function quit alot …especcialy on (cpu hungry) vst 's …But I wonder if I render the part like a dozen times or so ( adding new effects and stuff ) is there gonna be a loss of quality on the rendered sample ?Or can you render the selection as many times as you want without losing quality ?
Hardly any loss.
Renoise renders the selection to 32bit samples. So you should not worry 
It’s then more about what different vst’s might do to the quality of the sample.
However if you do a lot of pitching on the samples between renderings, then the resample and interpolation can be better if you render ‘offline’ (render to disk option) and use a better interpolation algorithm.