For numeric variables, you can't do that. A missing value for a numeric variable is displayed as a dot. The only thing you can do differently is to change how it gets displayed:
options missing=" ";
If you happen to have character variables that contain a dot, you can change them to blanks:
data want;
set have;
array chars {*} _character_;
do _n_= 1 to dim(chars);
if chars{_n_} = "." then chars{_n_} = " ";
end;
run;