Considering the following TeX document:
\documentclass{beamer}
\usepackage{tikz}
\usetikzlibrary{trees}
\tikzset{
invisible/.style={opacity=0},
visible on/.style={alt=#1{}{invisible}},
alt/.code args={<#1>#2#3}{%
\alt<#1>{\pgfkeysalso{#2}}{\pgfkeysalso{#3}} % \pgfkeysalso doesn't change the path
},
}
\begin{document}
\begin{frame}
\begin{tikzpicture}[overlay,remember picture,
level 1/.style={level distance=12mm,every child/.style={edge from parent/.style={->,solid,draw=blue}} },
level 2/.style={sibling distance=12mm,every child/.style={edge from parent/.style={->,solid,draw=blue}}},
level 3/.style={sibling distance=8mm,every child/.style={edge from parent/.style={->,solid,draw=blue}}},
semithick]
\node[draw=none,text=red] {S}
child[visible on=<2->] {node[draw=none,text=red] (a) {T}
child[visible on=<3>] {node[draw=none,text=red] (b) {L}}
child[visible on=<4->] {node[draw=none,text=red] (c) {K}}
};
\end{tikzpicture}
\end{frame}
\end{document}
The intention is to remove node 'b' and add another node 'c'. Both nodes needs to appear as the children of node a and appear at the same position.