If the file doesn't exist then this means there are no customised ranking or display settings for the profile.
the padre_opts.cfg allows you to set display and ranking settings (query processor options) that are combined and override what is defined in the query_processor_options line in your collection.cfg.
If there's no padre_opts.cfg in place when you apply the tuning raking settings then roll back is just a matter of removing the padre_opts.cfg which will hold the set of ranking parameters which were applied as a result of the tuning.