I have an issue where a customer wanted me to email an invoice. At the time the ticket was created the customer didn’t provide an email address. So the ticket was closed with no email address. I added in the email address but this only works for new tickets not previous closed tickets. Is there any way of updating customers details for closed tickets?
How have you setup the emailing part? How is it putting the email address?
I have email working in a couple of different ways but I mainly use print to pdf and then email. It has nothing to do with the email side of things because if you change phone number or address it will also use the original data. Only new tickets will use the changed data. If you type a phone number wrong or email address I cant see any way of changing the info on a closed ticket. I can understand why you cant change information on a closed ticket but for customer details there should be an exception.
Ok Ill explain better. How are you showing the email/number etc in the ticket? using {ENTITY DATA:X} or putting in with tag or something?
Not sure at the moment I will have to check tomorrow.
Just checked in database and can see a ‘EntityCustomData’ column which seems to be recording the entity custom data which is going to be at the time of the ticket/entity selection.
Not sure on a solution to that one sorry 
If you add new fields or change their names they wont update ‘old’ tickets, they will only take effect from new tickets
what you could do is also store the email address as a ticket tag for all new tickets and use that to send the email to your customer. you could also have 2 buttons mapped when you open/view the closed ticket such as “update email address” which will update the ticket tag with a new/amended email address, and “re-send invoice” which when pressed will send the invoice to the email stored as a ticket tag.
This way you could either open a settled ticket press the re-send button to re-send the invoice, or amend the email address first then press re-send
This would also work for previous tickets as your “update email address” button will add the ticket tag to which you can then press the resend button
Itll take a little work and automation to do it but i think this way should be do-able, youll just need to amend your current rule for sending an email from the {ENTITY DATA:Customers:Email Address} (of whatever your settings are) and change it to {TICKET TAG:Email Address}
I use this type of setup to update customers name on a bar tab and to add/update bar tab limits, so my two buttons change customers name and if their tab is set at £50 and their next set of drinks comes to £52 for example I could use my second button to override the bar tab limit to £55 to let the new items be added. All that is done just by using ticket tags and works very well, you should be able to adapt to your needs if it works how you want 
Hope that helps and gives you an idea