@DeeChRE: Once this group is created, can it be edited and reused for another transaction, or would that impact the previous transactions it had been used in? 

Yes, it can be edited as often as needed.

However, you don't really even need to do that if the group changes every time. Instead, set you can set up an empty group (or one that has only one or a few items that are usually included), use it on an invoice or other type of sales transaction, and then insert as many rows as needed within the group and add items right on the transaction.