first off all you should be using a plugin to do the rendering (izotope ozone or uv22 hr). just changing it to 16 and rendering is using the "stock" render and is not nearly as good. I also use the resampler 192 or crystal resampler plugin to resample.
I use the batch process to do both steps at once. I actually track the 24bit and then do the batch so the 16bit is tracked the same way. you can do the same process for the single file. I'm coping and pasting so this is for a tracked 24/48 but again you do it the same except it's one big file.
http://taperssection.com/index.php/topic,105212.msg1405831.html#msg1405831batch process in wavelab
open wavelab and go to tools > batch. then you should be on input. input the tracked 24 bit files. then go to output and point it to save in your 16 bit folder or wherever. also make sure that output is set to 16/44.
go back to input. there is a little box over to the right (between the A and extras buttons). that is the edit batch plugins button. click on it and then click on plugins > resampler 192 (or crystal). click on it. it should then move to the window on the left (sequence) . double click on it to be sure it's set to 44.1. then look back at the plugins and click on VST. select what you use to dither. I use izotope 3 most of you use uv22hr. so under sequence should be resampler first and then the dither tool. if you use izotope you must click on it to open it up and set up (turn on) the dither. you do not have to for uv22hr. always resample first then dither (make sure they are in the correct order and the first one is highlighted).
hit ok and then run and you will output 16/44 tracks from the 24/48 tracks.