\documentclass[a4paper]{memoir}

\makeatletter
\let\fixpdflayout\mem@fixpagelayout
\makeatother

\begin{document}

Teste - Página 1

\makeatletter
\clearpage
\setstocksize{250mm}{260mm}
\settrimmedsize{250mm}{210mm}{*}
\setlrmarginsandblock{0.79in}{0.79in}{*}
\setulmarginsandblock{0.79in}{0.79in}{*}
\checkandfixthelayout
\ch@ngetext
\fixpdflayout
\makeatother

Teste - Página 2

\makeatletter
\clearpage
\setstocksize{310mm}{290mm}
\settrimmedsize{270mm}{210mm}{*}
\setlrmarginsandblock{0.79in}{0.79in}{*}
\setulmarginsandblock{0.79in}{0.79in}{*}
\checkandfixthelayout
\ch@ngetext
\fixpdflayout
\makeatother

Teste - Página 3

\newpage

Teste Página 4

\makeatletter
\clearpage
\setstocksize{297mm}{210mm}
\settrimmedsize{\stockheight}{195mm}{*}
\settypeblocksize{671.6pt}{335.8pt}{*}
\setlrmargins{*}{*}{4}
\setulmargins{*}{*}{2}
\setmarginnotes{5mm}{45.23mm}{\onelineskip}
\setlength{\footskip}{3.0\baselineskip}
\checkandfixthelayout
\ch@ngetext
\fixpdflayout
\makeatother

Teste Página 5

\end{document}