:help 'backupcopy'
diz:
*'backupcopy'* *'bkc'*
'backupcopy' 'bkc' string (Vi default for Unix: "yes", otherwise: "auto")
global
{not in Vi}
When writing a file and a backup is made, this option tells how it's
done. This is a comma separated list of words.
The main values are:
"yes" make a copy of the file and overwrite the original one
"no" rename the file and write a new one
"auto" one of the previous, what works best
Parece que definir 'backupcopy'
como "sim" deve te dar o que você procura. Ou seja coloque isso no seu .vimrc:
set backupcopy=yes