Avoiding overprinted outlines with pdfrender when converted by Ghostscript

If I change the sequence of rendering the characters so they are overlaid then I see the following differences

using all 3 characters as one in my TeX viewer I see (same as you do later)

However If I overlay them I see this PNG produced and in my PDF preview

MWE

\documentclass[border=1pt,png={ghostscript,gsexe=gswin32c}]{standalone}
\usepackage{xcolor}
\usepackage{LobsterTwo}
\usepackage[T1]{fontenc}
\usepackage{pdfrender}
\begin{document}
\Huge\LobsterTwo\slshape
\textpdfrender{%
      TextRenderingMode=2,
      LineWidth=.01ex,
      StrokeColor=black,
      FillColor=yellow,
}{n}%
\textpdfrender{%
      TextRenderingMode=2,
      LineWidth=.01ex,
      StrokeColor=black,
      FillColor=yellow,
}{i}%
\textpdfrender{%
      TextRenderingMode=2,
      LineWidth=.01ex,
      StrokeColor=black,
      FillColor=yellow,
}{g}%
\end{document}  

Here is the result of running

gswin32c -dNoOutputFonts -sDEVICE=pdfwrite -o gstest_vec.pdf gstest.pdf

Note that with no color definition the screen result looks more like lime

As identified by AlexG many ligatures would probably break although a few may still work

This is not quite what you are after, but maybe you like it even more.

If you only stroke the glyph outlines by means of text rendering mode 5 (5 Tr), which also adds them to the clipping path, and fill an all-embracing rectangle with the desired fill colour afterwards, you get the following:

It is correctly converted to PDF with gs -dNoOutputFonts -sDEVICE=pdfwrite ... (glyph outlines retraced as graphic paths) and also to PNG.

\documentclass[border=1pt,png={ghostscript,gsexe=gswin64c}]{standalone}
\usepackage{xcolor}
\usepackage{LobsterTwo}
\usepackage[T1]{fontenc}

\begin{document}
\Huge\LobsterTwo\slshape
\color{yellow}
\pdfliteral page {0.5 w 0 G 5 Tr}%
nig%
\pdfliteral page {-88888 -88888 99999 99999 re f}

\end{document}