"Holy homework, Batman!"
What you're looking for is a way to search a string and replace, from the start of a string, a space that's as many as 50 characters in with a newline.
Now, if only perl had a mechanism to make this simple. And if only this mechanism had something called "quantifiers" you could use to specify your limit!
Wouldn't that be nice?
Please, click on the link above and read the perlre manpage. I'm going to post an answer behind spoiler space, but you'll do better in the long run if you read and understand the fine manual.