You cannot swap the operands. For example, with the given numbers, you cannot get the expression (1 + 3) * 2 = 8.

You need to add a digit only when it's needed, like from 9 to 10 or 99 to 100. In the cases you mentioned, there is no need to add one, only keep the same amount of digits. Not a kata issue.

Attention: If the number has leading zeros the amount of digits should be considered.