This gist allows to programmatically search and replace in latex taking in consideration word form.

xelatex-word-replace.tex

\documentclass{article}

\usepackage{xltxtra}
\usepackage{xecyr}
\usepackage{polyglossia}

\setmainlanguage{russian}
\setotherlanguage{english}

\newfontfamily\cyrillicfont{DejaVu Serif}

\usepackage{xesearch}
\usepackage{xstring}

\newcommand{\korabl}[1]{%
\StrChar{#1}{1}[\headchar]\StrGobbleLeft{#1}{1}[\tailstr]%
\IfStrEq{\headchar}{К}{С}{с}\IfStrEqCase{\tailstr}{%
{орабль}{удно}%
{орабля}{удна}%
{ораблю}{удну}%
{орабли}{удна}%
{ораблём}{удном}%
{ораблем}{удном}%
{ораблями}{удами}%
}[\tailstr]%
}
\SearchList{korabl}{\korabl{#1}}{корабл?}

\begin{document}

\section{Корабль}

Кратенькое описание использования корабля.

\end{document}