Is it possible to edit the cart/checkout process with flow?

[FurtherRecords]

Right now the only shopify flow triggers I see regarding the checkout are for after it completes. Is this correct?

Right now its only possible to have a single "Use this package to calculate rates at checkout" set up. I'd like to have perhaps 3 different shipping boxes that would be used depending on the size of the order.

I'd like to have something along the lines of: [trigger] items added to cart -> [condition] weigh items -> [action] select package used to calculate rates at checkout

[Jason]

That's not where Flow would come into play as there's not a "calculating shipping" or "customer moved to the shipping page" event that it has access too. The shipping rates would be something you could add unique logic too with the CarrierService API (or existing shipping apps that use that api)

I take it the shipping rules in Shopify that consider weight are not sufficient for your needs?

[FurtherRecords]

The weights of items are imported from a 3rd party data source. They're accurate enough - especially for 1-2 items. But when people buy the 20+ items the weight of the boxing required starts to add up. Not a big problem for domestic orders but when its an international order with express shipping the price difference is getting up there. Being able to add box weight would fix the issue most easily I think.