Yes, it's possible to adjust the price of the bundle from the cumulative prices of all the parts, @betefleming.

You can change the price of each item to change the price of the bundle.

1. Go to the Sales menu and then select Product and Services.
2. Find the item, then click Edit from the Action column.
3. Change the price of the product.
4. Select Save and close.

Since you also wanted to include a discount, you can create a discount item and add it to the bundle. However, we still need to enter the negative sign under the Rate column when creating a transaction.

You can follow these steps:

1. On the left pane, go to Sales.
2. Choose Product and Services, choose either Non-inventory or Service. 
3. Fill up the name and rate (e.g. 10%) of the item and all the necessary information, under Income drop-down select Discount given.
   
4. Click Save and close.
5. Under Product and Services, click the bundle and add then select +Add lines to enter discount item along with other items.
   
6. Hit Save and close.

In the invoice window:

1. Under Product/Service, choose the bundle. 
2. Choose the affected discount account, then under the Rate column input the negative sign before the rate/decimal number.
   
3. Once done click Save/Save and close.

Alternatively, you can simply add the bundle and then put the discount item together to an invoice.

Additionally, you can reference this article for more details on which type of item can be changed: Change product and service item types in QuickBooks Online. This contains a brief insight into adjusting inventory items.

If you have other concerns in regards to changing products and services and create a bundle, just tag me in your comment. I can assist anytime when possible. Take care and enjoy your day!