I assume the original expense transaction was not a single transaction split among different categories? Like you've paid for the restaurant one day then for the bills another day (entering two separate expenses in MoneyWiz?). If yes, you'd need to refund those transactions separately even if your friend paid you back with a single transaction. In financial terms, you should consider those transactions separate.
I agree in the transactional world BUT in the real world when I get paid back (refunded) I only get a single amount not multiple times.
So I need to somehow link the single incoming (refund transaction) to multiple outgoing transactions expense transactions.
I've being using this tool for 2 years now but I cannot see how you can achieve this. If there is please let me know.
Several other possible solutions:
1) Create a Rollup function (I've seen it in a few Accounts packages) - so you check-off each separate transaction as being refunded into a separate account and then highlight the individual transactions and roll them up into a single transaction
2) Create a Refund transaction type - where you can pick the individual transactions/categories that are refunded as part of this transaction
3) Do something fancy in reconcile mode