Student or Learner
If I want to present a separate piece of information along with a text, can “P.S.” and “by the way” be used interchangeably (i.e., Wish you a very happy birthday. May your shadow never be less. By the way/P.S., I will come tomorrow.) or will only one specific of the two be used?
As far as I know,
P.S.: The acronym of the postscript ;additional text added to a letter that has been completed and signed. Peope often use "P.S." when they are unable to change the entire text of the letter.
BTW=By the way simply means "in addition to what I was saying". Therefore, for your example I think "by the way" is appropriate.
[I'm neither a native nor a teacher If I'm wrong please correct me]