Regex是否只在文本不在空行之前的行上匹配换行符?

我试图用markdown换行符替换诗歌markdown文件中的换行符,这意味着在a)有文本和b)不在空行之前的行的末尾添加两个空格。

因此,以下文本:

this line should have a break
and this one
but not this one

and this one should
and this one
but not this one

and so on

将在X出现的位置添加两个空格:

this line should have a breakX
and this oneX
but not this one

and this one shouldX
and this oneX
but not this one

and so on

我的困惑似乎找不到正确的咒语。我想到的最接近的是 (.*?)\n(?!\n) 但它也匹配空行。