Not outside the function, no. Within the function, yes.

counter is useless, a simple input of (1011, 11) breaks your solution

Yes, it could, but I think deciding that for yourself is part of the kata.

You need to choose the strategy, if you can give back the change with one, then you can.

Thanks for that remark!
As you can see I am not a master of regex :D

You can use any operations from [adding, removing and replacing] operator that getting the desired word in minimum steps.
So answers for your questions are 1 (for adding) and 1 (for removing) respectively.