c:\@Work\Perl>perl -wMstrict -le
"print qq{version $]};
 ;;
 my $rx = '(?:(?i)b)';
 print qq{match x: '$1'} if 'aaBbBcc' =~ /($rx+)/;
 ;;
 my $ry = '(?i-mxs:b)';
 print qq{match y: '$1'} if 'aabBbcc' =~ /($ry+)/;
"
version 5.008009
match x: 'BbB'
match y: 'bBb'
[download]

(Same output under version 5.14.4.)

IOW, instead of storing the stringized representation of a  qr// object, define and store a string that represents a fully backward-compatible regex that can be compiled into a  m// s/// qr// object of any Perl version as needed. Or: why do you need to start with a  qr// that may tied, however loosely, to a particular version? That's the bit I don't grok.