I do this a lot:

Enter a manual transaction with the current date/time, trading token A for B. Wait to see what the resulting profit/loss is, and repeat until I get the P/L that I need. Then delete the transaction.

A feature like this would be very helpful:

Enter Wallet/A and Wallet/B and desired P/L. Run. No transactions created. Output would be the amount of A, the resulting amount of B, the P/L, and the cost-analysis, all using the current date & time. Maybe add a button to "Add transaction?"

As a further improvement, I would also like to limit the token selection by date: only sell tokens acquired before/after a certain date - in which case, if the net amount is not possible then Koinly would provide the maximum P/L possible.