Using pLaTeX with TexShop without setting it as default

Question

I am trying to use pLaTeX to compile documents in Japanese in TexShop. As far as I know, the easiest way to do it is to change the TeXShop Preferences from [Regular] to [pTex (ptex2pdf)], as demonstrated by the screen capture below.

However, when I set it into [pTex (ptex2pdf)], I can no longer compile documents I created under normal LaTeX setting (written in English). Do any one with pTex experience have similar issues before?

My preliminary thought is that: if one can toggle between LaTeX and pTeX in the same way between LaTeX, XeLaTex, and cwTex, things would become much easier. And I am wondering how other people solve this issue. Any thoughts would be greatly appreciated!

For the reference, here are the codes I want to compile:

\documentclass{jsarticle}[20pt]
\begin{document}
こんにちは！
\end{document}

Answer 1

Open ~/Library/TeXShop/Engines and duplicate the file XeLaTeX.engine, renaming it pLaTeX.engine.

Then open the new file with TextEdit so it contains

#!/bin/sh
platex  -file-line-error -synctex=1 "$1"

Just copy here and replace the contents.

Now, at the beginning of the file you want to compile with platex, add

% !TEX TS-program = platex

That's all: relaunch TeXShop and when you click on the Typeset button you'll get this console output:

This is e-pTeX, Version 3.14159265-p3.6-141210-2.6 (utf8.euc) (TeX Live 2015) (preloaded format=platex)
 restricted \write18 enabled.
entering extended mode

You can still select the pLaTeX engine from the drop down menu.