It is a little documented fact that a Text Expression created using the Menu Option Insert/Text can be editted by selecting the bullet at beginning of Text Expression then use Ctrl-E which 'Allows a single, selected item to be edited'. To my knowledge there is no other way, at the present time, to Edit a Text Expression once it has been created. It would be very handy to have a Meno Option to edit Text Expressions.
I do this all the time. Select the pimple in front of the text expression then either press ALT-Enter or goto Edit|Properties. It's as easy as that.
I found that if your text is too close to the Staff, it helps a lot if you "zoom in" and then select the diamond. I've used both methods Ctrl+E and the Alt+Enter.
As long as you do not highlight/select more than one text expression, it is fine to select other things in addition to the text and then Edit|Properties. You will still be able to change the expression text as long as only one Text Expression is in the selection.