Building on a similar question I asked, and its answer: Given that in reledmac a series (B below) of two-column critical footnotes can be made single-spaced in a double-spaced document according to the method below, how can a series (A below) of paragraph footnotes also be made single-spaced? Using the same method for A (which works for B) returns an error.
\documentclass[12pt]{article}
\usepackage[series={A,B},noend,noeledsec,nofamiliar,noledgroup]{reledmac}
\Xarrangement[A]{paragraph}
%\makeatletter % make A single-spaced: doesn't work
% \Xbhooknote[A]{\setstretch {\setspace@singlespace}}
% \Xbhookgroup[A]{\setstretch {\setspace@singlespace}}
%\makeatother % "unidentified control sequence" error here, if lines are uncommented
%\let\footnote\footnoteA
\Xarrangement[B]{twocol}
\Xcolalign{\justifying}
\makeatletter % make B single-spaced (no errors)
\Xbhooknote[B]{\setstretch {\setspace@singlespace}}
\Xbhookgroup[B]{\setstretch {\setspace@singlespace}}
\makeatother
\let\footnote\footnoteB
\usepackage[doublespacing]{setspace}
\usepackage{lipsum}
\begin{document}
\beginnumbering
\pstart
\lipsum*[1]\edtext{Lipsum}{
\Afootnote{\lipsum*[3]} % paragraph footnote: needs to be single-spaced
\Bfootnote{\lipsum*[4]}} % two-col footnote: is single-spaced
\lipsum*[6-7]
\pend
\endnumbering
\end{document}