$t = "1,2,3,4\n8,9,10,11\n7,8,9,10,\n12,13,14,15\n";;
print $t;;
1,2,3,4
8,9,10,11
7,8,9,10,
12,13,14,15

$t =~ s[(\D|^)(?=\d(?:\D|$))][${1}0]g;;
print $t;;
01,02,03,04
08,09,10,11
07,08,09,10,
12,13,14,15