Find/replace in TextEdit

Copy the each paragraph of the document. Paste it in the browser address bar. Copy it again from the address bar and paste it in your document. The outcome for each paste should be that part of the document on single line. Will only be practical of course if you have limited number of paragraphs.

I think this answer here is what you're looking for:

How does Mountain Lion set the default text editor for the "open -t" terminal command?

To change default text editor to e.g. textmate, execute this command in terminal then restart:

    defaults write com.apple.LaunchServices LSHandlers -array-add 
'{LSHandlerContentType=public.plain-text;LSHandlerRoleAll=com.macromates.textmate;}'