Pgfplotstable has styles like every row no <index> and some other styles as well.
However, these styles are applied quite late in the processing: the content is already fixed at that stage.
I accept this as a feature request.
However, there is a simple way to enable such a style: the styles named every row <rowindex> column <colindex>. These styles allow changes to the content generation, in particular, they respect changes to the number format.
You can group a sequence of such styles to change all values of a specific column easily using
\documentclass{article}
\usepackage{pgfplotstable}
\begin{document}
\pgfplotstableset{
% #1 = row index
% #2 = row style keys
row style/.style 2 args={
every row #1 column 0/.style={#2},
every row #1 column 1/.style={#2},
every row #1 column 2/.style={#2},
every row #1 column 3/.style={#2},
every row #1 column 4/.style={#2},
every row #1 column 5/.style={#2},
every row #1 column 6/.style={#2},
every row #1 column 7/.style={#2},
every row #1 column 8/.style={#2},
every row #1 column 9/.style={#2},
every row #1 column 10/.style={#2},
}
}
\pgfplotstabletypeset[
row style={3}{sci},
]{
a b
0 0
1 1
2 2
3 3
4 4
5 5
6 6
7 7
8 8
9 9
10 10
}
\end{document}
EDIT: concerning your second question: you wanted to format percentages (i.e. to multiply with 100 and to append '%'):

\documentclass{standalone}
\usepackage{pgfplotstable}
\begin{document}
\pgfplotstabletypeset[
columns/A/.style={
column type=r,
preproc/expr={100*##1},
postproc cell content/.append style={
/pgfplots/table/@cell content/.add={}{\%},
},
fixed,
fixed zerofill,
},
]
{
A
0.01
1
0.1234
0.5
}
\end{document}