So, the following question was sent to the beamer mailing list, and after spending over an hour trying to answer what I thought would be a trivial question, I figured I might as well put the answer here. (I'm going to feel very silly if this turns out to be a duplicate.) The idea is that you start with something like this:
\documentclass{beamer}
\let\Tiny\tiny
\setbeamertemplate{navigation symbols}{}
\begin{document}
\frame{
\begin{itemize}
\only<1> {
\item Foo
\item Bar
}
\only<2> {
\item I replace Foo
\item I replace Bar
\item I am new!
}
\end{itemize}
}
\end{document}
Now, since they are of different sizes, this makes the itemize jump around on the slide. We need some grouping of the items that reserves space for the contents of the largest group.
<1>
it wasFoo\\second line
, and in<2>
still only one line, does the solution still work?