#! perl -sw
use strict;

s[(?:\S+ ){2}\K((.).(..))][$2Y$3 $1], print while <DATA>;

=output

C:\test>junk56
col1 col2 cYl3 col3 col4 col5
1234 5678 9Y12 9012 3456 7890

=cut

__DATA__
col1 col2 col3 col4 col5
1234 5678 9012 3456 7890