🚀 go-pugleaf

I don't see the same behavior that your describe.  

:%s/^/string/ appends "string" to the beginning of every line just fine
on my machine.

It is possible to imbed carriage returns and write them to disc, but vi
seems to truncate lines containing carriage returns when reading them
back in the next time.  However, :set notosscr makes ed treat the
carriage return as any other character, including displaying the line
terminating cr prior to the lf.  Type ":set all" to see all of the
options.

I am not familiar with the :o command of which you speak, but the MKS vi
that I have and the UNIX vi that I have both behave and respond the same
way to the limit that I played with them.