Long lines
My favorite editor is TxEd. It edits anything I can load in its memory,
even binaries. I tested a file with lines 4000 characters wide, and it
works okay. TxEd is a commercial product available from MicroSmiths or
your dealer.
ARexx is also capable of "editing" if you don't need to see what you are
doing. If you are trying to do a global-search-and-replace on a monster,
it is straightforward to write an ARexx program to do that. ARexx is a
commercial product, which is provided free with version 2.0 of the Amiga
operating system (if you happen to already own an A3000). Otherwise, it
lists for either $49.95 or $50.00 (I can't remember whether Bill Hawes is
charging the extra nickle for ARexx or for WSHell).
Icon is another string-oriented programming language. If your project is
complex, it may be easier to teach yourself enough Icon to write a "read a
line, munge it up, write a line" program than the equivalent ARexx program.
Icon is available here in the Other Languages Data Library.