Allow existing customers to edit their contact info

Hi Greg,

I realise this is quite an old issue now, but I required this functionality too. I've attached a very basic patch that provides this functionality. Hopefully it can be of use to someone else too.

Turned out that we are running this in production for a good five years now! So +1 for RTBC from me.

Created a merge request with the patch from #2.

I apologize if this is not the best place for this, but I wanted to say

A) thank you for the patch and
B) although I recognize everything discussed here is for Commerce 8.x-2.x-dev, I am using 3.0.1 as of today and I updated the patch to handle a difference introduced in 3.x in this commit to OrderRefresh.php in 2021. Every time the order is refreshed, the email address for the authenticated user is syncd with the order email, which totally makes sense most of the time. But it doesn't make sense if you're allowing existing customers to update their contact info during checkout, so here's an quick updated patch that comments out the relevant bit in OrderRefresh and includes the rest of the changes provided in the original patch adjusted for a few other insignificant changes for anyone who finds this and is using 3.x.

Instead of commenting out the part where the order email is synced, perhaps we should flag the order from the pane?
So basically, something like:
$order->setData('customer_email_overridden', TRUE);

This way we could skip the email refresh, when this data flag is set?

That is much better in every way. Thank you so much!!

I'm wondering if I should only set the data flag for logged in customers. Perhaps no need to store extra data for anonymous customers... What do you think?