Option 1  You might need to configure a separate delivery route with route selection on sales order line, based on customer this route can be selected at time of order. Also there is likely to be an associated stock move/ operation from GF/B2C (main sock) to B2C Showroom Credit Location (delivery location) for these customers

Option 2 Other alternate to achieve this could be to create a separate delivery Warehouse for these customers which you could select in other info tab on a sales order/ Quotations at time of order. Set Resupply From on delivery WH to main WH

Option 3  Create a new customer location and update in contact

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Option 1

Select route from sale order line

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Option 3

1. Create a new customer location


2. Create the delivery route for this customer location



3. Change the customer location for contact on the sales and purchase tab. You would need to be on developer mode to view this



 

On sale to this customer delivery route is auto created