Redefining default rule

Hello,

I would like to redefine the flex default rule "unmatched scanner input is 
echoed to stdout" into another rule.

I tried this : <*>.      { action_to_be_taken;}
but at compilation time, it says : bad start condition name and bad start 
condition list.

when I declare this rule with all the start conditions that I have (30) 
<s1,s2...s30>, it is ok, but it is not the nicest way to declare this....
Hence I'd like to know if it is possible to redefine the flex default rule. 
If yes, how should I declare it?

Thanks in advance for your help!