You might find some of these online demos or code snippets useful.
However, in principle you might want something like:
if key_resp.keys == 'r':
condFile = 'rabbits.xlsx'
animal = 'rabbit'
else:
condFile = 'birds.xlsx'
animal = 'bird'
Then use $condFile for your trials look and your instructions
might look something like
$'Press the space bar whenever you see a '+animal+'.\n\nPress the spacebar now to start.'