# Best workflow for inserting an additional step into an animated tikz picture?

I have some old beamer slides that contain an animated tikz picture with a bunch of \only<4->{} commands and the like. It's a fairly complicated picture with many slides and illustrations. Now I'd like to insert an additional slide immediately before step i.

What would you suggest as the best workflow for this?

Essentially, what I want is to add +1 to all overlays that involve slides above i, but not those before. If an overlay starts before i and ends on or after i, I want to keep its start unchanged and add +1 to its end slide.

Here is a MWE. The first frame shows a simple animation, and the second one inserts one more step just before step 2.

    \documentclass[]{beamer}

\usepackage{tikz}

\begin{document}

%from this:
\begin{frame}\frametitle{before}
\begin{center}
\begin{tikzpicture}
\draw[arrows=<->] (10,0) -- (0,0) -- (0,6);
\coordinate (n1) at (8,2);
\coordinate (n2) at (1,5);
\coordinate (n3) at (5,4);
\only<1>{\draw (n1) circle[radius=3pt] node[below left] {$x_1$} ;}
\only<1-2>{\draw (n2)  circle[radius=3pt] node[below left] {$x_2$};}
\only<3>{\draw (n3)  circle[radius=3pt] node[below left] {$x_3$};}
\end{tikzpicture}
\end{center}
\end{frame}

%to this:
\begin{frame}\frametitle{after}
\begin{center}
\begin{tikzpicture}
\draw[arrows=<->] (10,0) -- (0,0) -- (0,6);
\coordinate (n1) at (8,2);
\coordinate (n2) at (1,5);
\coordinate (n3) at (5,4);
\only<1>{\draw (n1) circle[radius=3pt] node[below left] {$x_1$} ;}
\only<1-3>{\draw (n2)  circle[radius=3pt] node[below left] {$x_2$};}
\only<4>{\draw (n3)  circle[radius=3pt] node[below left] {$x_3$};}