Preorder Order Editing
Send invoices to customers that added products to their order, but haven't paid.
Shopify Flow
Send customers an invoice reminder after they've saved unpaid edits to their order.

How it works
Shopify Flow Actions can be triggered to programmatically control which of your customers are allowed to edit their orders. Customers that can't edit orders won't be notified that editing an order is a possibility through email marketing. If a customer tries to edit an order that's recently has it's editing disabled, they'll be brought to an order status page instead to track their order.
Idea: Disabling edit for high risk orders
You can create a new Shopify Flow that is triggered each time a new order is created. If an order is created with a high-risk of fulfillment, you could hold the order until you reach out to the customer. For all of those customers you could automatically disable order editing to prevent customers from changing product quantities or purchasing more products in the upsell options because they have already bene identified as high risk. For all other orders that aren't high-risk you can immediately release the order for fulfillment.
Idea: Allowing infinite preorder edits
Your store might be selling pre-orders products with weeks or several months of being on a fulfillment hold until there is inventory to ship those product orders. You could define a tag on Shopify admin like 'preorder' and create a Shopify flow that doesn't disable order editing for those orders until the order has shipped. This gives customers several more opportunities to add products to their order up until their entire order is ready for shipping.
How It Works:
Every order has a metafield, orderediting.editing_cutoff_date, that sets the date when editing is no longer available for an order.

When Shopify Flow calls the Order Editing action to enable order editing, the order's order editing cutoff date increases by seven days. When edits are disabled the cutoff time is set the timestamp of when the Shopify Flow action was triggered which will prevent all future customers signing into their order editing portal from editing their orders.
Common Questions
Q: What if I have multiple Shopify Flow templates running?
A: Order Editing will respect the last event received by your Shopify Flow templates. If you disable, enable, and disable order editing on an order in rapid frequency the last event would determine the cutoff date for the order. You can also edit the date yourself, without using Shopify Flow, in the metafields of each of your orders.
Q: Are customers notified each time order editing is enabled?
A: No. Enabling or disabled order editing does not trigger any emails.