Need a Grep Expression for changing a space between braces.

Hey All --

I know this has got to be ridiculously simple for anyone that knows Grep.

I have a string of text in braces like this:

{namevalue="Firstname Lastname”}

And I would like to add any special character or word between the first and last names so I can make some additional changes to the structure via find/replace.

So I would like to change it to this for example:

{namevalue="Firstname$$$Lastname”}   or this: {namevalue="FirstnameKAPOWLastname”} or this: {namevalue="Firstname12434Lastname”}

You get the picture. Any assistance will be greatly appreciated.