Is there a way to replace select * fields in result ?

Hello,

Is there a way to replace select * fileds in result ?
I have select qw.* from table but I want field for example mm to be 
replaced with custom value like:

select qw.*, case whem length(qw.mm) > 0 THEN COALESCE(SUBSTRING(qw.mm, 
1, 1), '') ELSE qw.mm END AS qw.mm

Is there some way to do that ?

Regards,
HS