Once upon a time, when I used a WYSIWYG word processor, I took a completed document and used Find-Replace to turn all instances of "." into tiny smiley faces. It wasn't really a difference that anyone would notice, but if you printed with a good printer and looked closely, it was there. Each sentence was slightly more joyful, for me at least.
I'm interested in repeating this in LaTeX. My initial stab:
\documentclass{article}
\usepackage{wasysym}% For the smiley character
\usepackage{lipsum}
\catcode`\.=\active% Make . an active character
\def.{{\tiny\blacksmiley{}}}% Make . expand to a black smiley
\begin{document}
\section{A Section}
\subsection{Stuff}
Some text. A number: $3.14$. \lipsum[1]
\end{document}
The results are mediocre. The tiny smiley is too large, and will of course remain \tiny even in the middle of \tiny text. The decimal which appears in the subsection label (1.1 Stuff) and the periods in the lipsum text also remain normal periods.
It seems that the better way of doing this would be to define a custom font where the period character is defined as being a black smiley. Is there a way of doing this within LaTeX - that is, saying "load this font, then modify it by redefining the period character as scaled-down version of this black smiley character from another font" ?
In this related question [ Replacing a glyph in one font with a glyph from another ], the asker wanted to replace the double-storey "a" and "g" with single-storey versions. The comments suggested that it's possible, but that the kerning would have to be redefined and this would be an enormous pain. This case is a little different because the replacement character should have the same size and shape as the original - i.e., the kerning of the original period would work perfectly for the replacement smiley.

\tinysmiley directly from a font, a scaled version could be created with\scaledboxfrom thegraphicxpackage. – barbara beeton Oct 17 '14 at 20:31