\documentstyle{article}
\font\cmr=cmr10
\font\cmrxvii=cmr17
\font\tenps=ptmr at 10pt
\fontdimen33\tenps=1pt
\font\twnps=ptmr at 40pt
\fontdimen33\twnps=1pt
\let\oaccent=\accent
\let\accent=\char
%\def\accent{\ifnum\fontdimen33\the\font >0\message{builtin}\char\else\message{oldstyle}\oaccent\fi}
\tracingmacros1
\begin{document}
Let's try some stuff: {\cmr resum\'{e}},,, {\tenps resum\'{e},
resum'e, resum\char19{e}, resum\char19e},,, {\twnps resum\'{e},
resumé, resum'e},,,resum\'e.

\aa {\cmr \aa{}ngstrom} {\tenps \aa{}ngstrom \char23a{}ngstrom \oaccent23a{}ngstrom} {\twnps \aa{}ngstrom \char23a{}ngstrom \oaccent23a{}ngstrom}

{\twnps
acute: \'{o} \'{e} \'{i} \'{u} \'{a}
grave: \`{o} \`{e} \`{i} \`{u} \`{a}
circum: \^{o} \^{e} \^{i} \^{u} \^{a}
diresis: \"{o} \"{e} \"{i} \"{u} \"{a}
tilde: \~{o} \~{e} \~{i} \~{u} \~{a}
\let\accent=\oaccent
overbar: \={o} \={e} \={i} \={u} \={a}
%dot: \.{o} \.{e} \.{i} \.{u} \.{a}
uthing: \u{o} \u{e} \u{i} \u{u} \u{a}
vthing: \v{o} \v{e} \v{i} \v{u} \v{a}
\let\accent=\char
%hungarumlaut: \H{o} \H{e} \H{i} \H{u} \H{a}
tie: \t{oo} \t{oe} \t{oi} \t{ou} \t{oa}
cedilla: \c{o} \c{e} \c{i} \c{u} \c{a} \c{c} \char24c
underdot: \d{o} \d{e} \d{i} \d{u} \d{a}
underbar: \b{o} \b{e} \b{i} \b{u} \b{a}
slasho: \o \O
}
{\cmrxvii \t{oo} \t{oa} \o \O}
\end{document}
