Thanks, editing the sequence file in notepad++ has made the steps editable again.
Not the solution I was hoping for, but actually global replace made it easy.
I tried setting the read only flag on a test step and got a warning that the flag was a one way setting that could not be undone - so that explains the greyed out box.
Still no idea how it got set in the first place, but this code has had a busy past and if no one else has the problem I guess I will stop looking for the reason.
