With the help of a great answer to https://tex.stackexchange.com/a/50706/13904 I was able to redefine the \cite command as:
\renewbibmacro*{cite}{%
\iffieldundef{shorthand}
{\ifthenelse{\ifnameundef{labelname}\OR\iffieldundef{labelyear}}
{\usebibmacro{cite:label}%
\setunit{\addspace}}
{\printnames{labelname}%
\setunit{\nameyeardelim}}%
% \usebibmacro{cite:labelyear+extrayear}}% DELETED
\printtext[brackets]{\usebibmacro{cite:labelyear+extrayear}}}% ADDED
{\usebibmacro{cite:shorthand}}}
But a problem appears when one has multiple citations of a same author.
\cite{Hembree88,Hembree90}
gives
HEMBREE 1988HEMBREE 1990
instead of
HEMBREE [1988; 1990]
Any idea how to solve this?
Here is a working example:
\documentclass{article}
\usepackage[english]{babel}
\usepackage[style=authoryear-icomp]{biblatex}
\makeatletter
\renewbibmacro*{cite}{%
\iffieldundef{shorthand}
{\ifthenelse{\ifnameundef{labelname}\OR\iffieldundef{labelyear}}
{\usebibmacro{cite:label}%
\setunit{\addspace}}
\printnames{labelname}%
\setunit{\nameyeardelim}}%
\printtext[brackets]{\usebibmacro{cite:labelyear+extrayear}}}% ADDED
{\usebibmacro{cite:shorthand}}}
\makeatother
\usepackage{filecontents}
\begin{filecontents}{\jobname.bib}
@misc{A01,
author = {Author, A.},
year = {2001},
title = {Alpha},
}
@misc{A02,
author = {Author, A.},
year = {2002},
title = {Alpha},
}
\end{filecontents}
\addbibresource{\jobname.bib}
\begin{document}
\cite{A01,A02}
\printbibliography
\end{document}

authoryear-icompcitation style, but the code snipppet from the linked answer is suited for theauthoryearstyle. But more important, you didn't describe in detail the results you want to achieve. Do you just want to replace parentheses with brackets, or is it something more complex? – lockstep Apr 30 '12 at 22:33