In Hackman, you can just select (click on) the value you want to change and type the new value.
Other hex editors may require a right click or double click on the value to bring up an edit box, or may open files in read-only mode by default, requiring an option be changed for editing. If you are using Hackman, try again; if not, check the help file.

PS when you go to the wastelands, your quest log gets cleared. This could just be cosmetic, but you may or may not be able to complete previous quests after returning to Rivertown this way.