My experience of the OP’s question is no, you can’t re-open a cancelled order.
I had a Tiguan on order early last year that was delayed by Covid, while waiting for it to arrive my leased Yeti was written off by a man in a van. I rang round trying to find a Tiguan and my local (Newcastle) dealer said they had one, they cancelled the original Motability order (which was with JCT in Wakefield) then rang me 2 days later and said they didn’t really have one at all and hadn’t placed the order with Motability 🙁
I rang Motability straight away and the short answer was once an order is cancelled it’s gone. A new order has to be placed at current AP rates etc. In my case they wouldn’t accept an order until they fully re-opened on July 1st, the AP by then had massively jumped to almost double to £2995 so no Tiguan 🙁
Please excuse spelling/typos. Apart from being a clot it turns out I had one on my cerebellum that's now causing various problems!