Just got in to loads of emails.
I have been cleaning a roof on an old Budgens in Heathfield - W Sussex, that will be a Sainsbury's on Tuesday morning!!!!.
As mentioned really. I am fortunate to have dry steam, hot box and a recent purchase from Roger
I would say that the info given is sound and should be followed.
I would only add that if you can offer the client the removal, clean & re glue before the store reopens this may look better than just I'll do what I can.
Make sure you know what you are going to be re gluing them with before removal. That is if dry steam is not an option.
Good luck
Rob