It's been some time since I used the ProcessBook Support Tool, so I wouldn't know any tricks there. But you could definitely do this in ProcessBook if you write a small VBA script.
Open the PI ProcessBook Programmer Reference Guide from the help menu, and navigate to the MultiState section. There you will see an example on how to use this, and you should be able to read out the current config string using MultiState.GetPtTagName, then manipulate the string (replace the old name with the new), and then set it using MultiState.SetPtTagName.
Loop through all the symbols in the display and use MySymbol.GetMultiState to find all the multistates.
You can either add this code directly to your display and activate it using a button, or you can create another display which acts as a "renaming application" and then add the code to change any other open displays in your current ProcessBook session.
Another way to achieve your goal might be to save your display as .SVG, then open it in a text editor and do a find/replace there. Then you can open that .SVG in ProcessBook and re-save it as PDI. Please note that any VBA code will be lost during this transaction so make sure you're working on a copy of your display so you have backup.