public RussianStemFilter(TokenStream in,
    char[] charset) 
{
        
        super(in);
        stemmer = new RussianStemmer(charset);
}

 public final Token next() throws IOException 
{
        if ((token = input.next()) == null)
        {
            return null;
        }
        else
        {
            String s = stemmer.stem(token.termText());
            if (!s.equals(token.termText()))
            {
                return new Token(s, token.startOffset(), token.endOffset(),
                    token.type());
            }
            return token;
        }
}

 public  void setStemmer(RussianStemmer stemmer) 
{
        if (stemmer != null)
        {
            this.stemmer = stemmer;
        }
}

Set a alternative/custom RussianStemmer for this filter.