If you don't know anything about that tool than you won't mind using something else? How about a simple shell command?
Here is the same operation in Bash in increasing level of genericity. You probably don't care for the first two as it has hardcoded yyy's and zzz's but I did it to show you around the sed command a bit to understand the third one.
for file in * ; do mv "$file" "$(echo $file | sed 's/a - yyy/-pt1/g')"; mv "$file" "$(echo $file | sed 's/b - yyy/-pt2/g')"; done
for file in * ; do mv "$file" "$(echo $file | sed 's/a - .*.zzz/-pt1.zzz/g')"; mv "$file" "$(echo $file | sed 's/b - .*.zzz/-pt2.zzz/g')"; done
for file in * ; do mv "$file" "$(echo $file | sed -r 's/a - .*.([a-z]{3})/-pt1.\1/')"; mv "$file" "$(echo $file | sed -r 's/b - .*.([a-z]{3})/-pt2.\1/')"; done
There must be many other ways with other commands, of course.
You'll get unimportant errors because the mv is done twice on the whole batch.