I wasn't entirely sure either, I checked it in Openoffice, not Excel

Can a formula append text to the contents of its own cell? Would that not introduce a circular reference?

It seems to me that an additional column is needed, say in F12, with something like:

Then you could hide column E.

My Excel is very rusty though, so there may be a much better solution.

Edit: a better solution like a VBA macro, but my knowledge of those is even more rusty!