You should be able to do it, in mendix 8 and 9.
Don’t forget to put your constant with expose to client to yes.
it is not possible to directly use constants in text. As you can see here: https://docs.mendix.com/refguide7/constants.
You might be able to 'hack it’ by creating some sort of nonpersistent helperentity with a string attribute which contains the text you want to show. This string can be filled in a microflow, a datasource microflow for example, with the constant value.