Since you're seeking help, you'd better explain what you mean by "change my previously greedy quantification into a possessive modality" -- perhaps with a description of your intent that actually provides comprehensible information. And it wouldn't hurt to show a (small) sample of your data and your desired output (and possibly, explain why the last part of the code sample in para 1, ($meanSearchTerm) doesn't match the error message you posted.
BTW, Perl 5.14 on win7 executes your sample (minus the ($meanSearchTerm) without squawking:
C:>perl -e "my $foo='123.123';$foo =~/(\d++\.\d++)/oi; print $1;"
Update/afterthought: I was actually well started writing an explanation of why that wouldn't compile when I decided to check. Once again, testing saves my butt.