The answer depends on what you want to do.
First of all changing your filenames does not mean that you need to change your URLs. These are two different systems of referring to objects; Filenames refer to server files, and URLs refer to Web resources. The two need not be similar in any way, despite the fact that by default, the server maps URLs to filenames in such a way that the last part of the URLs and filenames look identical.
In brief, you can easily keep the old URLs and simply rewrite requests for those old URLs to the new filenames on the server. The links on your pages don't change, search engines see no difference, and you don't affect your page ranking or visitor's bookmarks in any way -- Again the URLs are not dependent on the server filepaths.
This is accomplished using the "internal rewrite" function of mod_rewrite, which can map requested URLs to arbitrarily-chosen server filepaths.
If you really want to redirect all those old ranked, listed, and bookmarked URLs, then 50 redirects, one per line, is the proper way to do it.
Note that if there was some organized, systemic change to your file organization, it is often possible to redirect (or rewrite) entire groups of old URLs to new URLs, using the magic of regular-expressions pattern-matching.