There's really no need to do a separate match and substitution, just change the pattern that the substitution matches:

s/^((?i:ORACLE_SID|ORACLE_HST_SID|ORACLE_HOME|SDP_HOME))(?==)/(my $lhs
+=$1) =~ tr:_:.:; $lhs/e for @envArray;
[download]

(update: corrected the missing parens, as per Roger_B's update)