Here is a simple datastep that does the job. Less sophisticated than @FreelanceReinh 's suggestion but it should provide a good starting point :
data want;
set have;
array x George -- Many_more_name;
do i = 1 to dim(x);
if upcase(vname(x{i})) = upcase(select_person) then do;
x{i} = 0.8 * x{i};
leave;
end;
end;
drop i;
run;
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