Is that in the Sheet View or the Plan View?
Elevate Lines should work in the Plan View and I have used it with partial success in Sheet view. In the Sheet View you will see the No Entry Sign when you go to select the Text Item(s) or line item(s) however if you click in the grey space at the base of Project Explorer or View Filter Manager then you can actually select the text and Lines in the Plan Sheet View and it will elevate the line using the 11.00 out of the Datum Label. If you are running Multisheet View in Sheet View that is where I have seen issues that I had to double check what it did and it screwed up in a few places - I have not had time to validate that though.
Those commands will read the numerical values out of the text string so that Datum: 11.00 would be read as 11.00 for elevating purposes. The elevation should be added to the nearest line where the insert point of the text is nearest to the line that it selects to use (based on the search radius tolerance in the Elevate Lines command.
There is no tool that I know of that can search and replace in Text Items - I will add it to the list of Tools
Alan