Having used another Edit Order app to modify our invoices, I had high hopes when I download Lopster because of its claim that they don't duplicate the existing invoice before saving a new one. That may be the case but, unfortunately, Lopster does not allow any modification of the shipping charges.
I have tried on three separate occasions to get help from the Developer. I contacted the Developer thru the normal App support channel. On all occasions, there has be NO reply. That's unacceptable. Buyer beware.
I have removed this App.

Initially worked better than other order edit & exchange apps, that have created ghost orders and messed up our admin. But causes strange anomalies.
But increasingly often it doesn't load. I have NEVER had a support request answered (of 8 now, I believe).
Edit: We have now delete it and caused more issues than it solved.

We used Lopster to edit orders after customers wanted to change their size.

The app didn't retrieve the existing orders and kept showing ERROR 404. Using Editify instead was a quick option so we didn't bother finding a solution with customer support. 2 stars cause the app has an accessible price.