Please excuse me for ancient history but I just have to get it off.  I use an old version of Nisus 4 that has the nice property that all formatting is in the resource fork and the data fork has just text - text that could be an executable shell script.

I do assembly language programming on tiny microprocessors and I need a listing format to handle columns some of which are one character wide and typically end with a long string that is a comment. Single tabs separate the data into the columns which makes them importable into Excel.

I created a blank Nisus document with the format I want in its resource fork. My assembler can put out its listing by making a copy of the Nisus file and storing new data in a new data fork. It works fine and those comments will wrap to another line beginning the continuation at the left end of the rightmost column. I can have constant width text in the commands and variable in the comments.

BBedit won't do that. All columns have to have the same width! TextEdit is hopeless. VIM is worse.

That's why I keep this OS 9 machine running.  It's also why I quit upgrading Nisus.

It just might be possible to create a new Nisus document with the desired columnar format. With some trickery you could replace the text in that document with the text you want but it isn't as simple as providing a new data fork. Is the format of a Nisus file available so that one might work out an AppleScript? Might the formatting be in a well known part of the file that could be copied into a text file with no word by word markups?

It just might be that a spreadsheet would have more formatting capability than the current Nisus. That might solve  the OP's problem.

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-->  The best programming tool is a soldering iron <--