MATL, 11 + 14 = 25 (safe)
'tacocat'0y Current output:
tacocat 0 tacocat Desired output, adding 7 bytes:
taataccocaccoaaat Intended solution
'tacocat'0y"@Yfh]) Forgot about this challenge for a while. Explanation:
'tacocat' % Push the string 'tacocat' y" ] % Loop over copy of this string @Yf % Calculate prime factors of each ASCII code point 0 h % Concatenate factors, with initial zero ) % Index (modularly) into the original string. Implicit display.