scrlttr2: change vertical spacing before signature

Question

How do I change the vertical spacing before the signature in scrlttr2 without editing lco files?

Per the KOMA-Script documentation, \@setplength{sigbeforevskip}{length} seems to do what I need, but \@setplength is not allowed in document files, only in lco files. I'd honestly rather not fiddle around in those, partly because I would need to figure this out again when I get a new machine, whereas including a line like this in my letter tex template would be easy.

I tried adding spacing commands to \setkomavar{signature}{\usekomavar{fromname}}, but those were eaten and did not change anything.

(Why do I want this at all? I find the default spacing too cramped to add my handwritten signature above the signature.)

MWE:

\documentclass{scrlttr2}
\usepackage{blindtext}

\setkomavar{fromname}{Foo Bar}
\setkomavar{signature}{\usekomavar{fromname}}

\begin{document}
  \begin{letter}{Baz}
    \opening{\dots,}
        \blindtext
    \closing{Best regards}
  \end{letter}
\end{document}

Answer 1

Starting with KOMA-Script version 3.26 you can use \setplength (without @):

\documentclass{scrlttr2}
\usepackage{blindtext}

\setplength{sigbeforevskip}{2cm}% needs version 3.26 or newer

\setkomavar{fromname}{Foo Bar}
\setkomavar{signature}{\usekomavar{fromname}}

\begin{document}
  \begin{letter}{Baz}
    \opening{\dots,}
        \blindtext
    \closing{Best regards}
  \end{letter}
\end{document}

With older KOMA-Script versions you can use in the document

\makeatletter
\@setplength{sigbeforevskip}{2cm}
\makeatother