[TYPO3-dev] How can I change the text "Login-error or session timed-out"

[Christopher]

Hi guys,

I want to modify this message:
"Login-error or session timed-out No user logged in! Sorry, I can't proceed 
then..."
The text comes from t3lib/class.t3lib_beuserauth.php, line 191.

Now I could simply change the text, but if I do so, this change will be lost 
after the next upgrade.

Maybe there is the possiblity to use a hook in order to use str_replace() on 
the output?

Or are there other possibilities?

VG

Christopher