While Shopify does allow formatting your order IDs, and while you can change that format whenever you wish, the order ID formatting rules apply to all incoming orders. And, once set, an order ID cannot be changed.
If the ability to set this would be useful for you, we encourage you to contact Shopify and let them know. :)
Under the hood, this value is known as the order's
name (see docs). This is a read-only property. This is different than the order's
order_number property (which does not include the formatting rules mentioned above), and different further than the
id properties, both of which are internal references for the order.