You have a copy, make the changes in your copy of the fe and send it to the customer.
Am I alone in this world who maintains databases to his customers or am I missing something?
No - I maintain my client databases
In all cases I have the master copy and make changes to that then either:
Send the client a copy via email
use remote desktop to install it myself
use skype/zoom to install via that instead
Other options I've used in the past similar to skype/zoom are teamviewer and jump desktop
I also use last 2 methods when a client asks for a one-off requirement outside the scope of the app I provided.
Oh, and I have one client who is only 20 mins away - I have remote desktop for them but occasionally will pop round and work on one of their machines.
I sometimes wrap the app up in an installer package for new apps - depends on the requirements.
How do you imagine you would support your client?