Use "replace with regular expression" on many albums at once

I have several series of albums with names like these:

demos - pc (a)
demos - pc (g)

And which in this case runs in an alphabetical sequence from a to g, otherwise identical.

What I'd like to do is to add a prefix string to the album names, but don't want to have to do it for each one. I thought of using a "Replace with regular expression" with this:

^demos - pc (.)$

But how do I format the replacement string so that the letter in brackets (the ".") is preserved? As far as I can tell, the replacement string is a literal string.

I can hardly see a difference ...
if you want to keep the "." in brackets but it is variable then a construction like
search: ((.))
Replace: ($1)
would work...

This should work ...

Action .....: Format value Field ......: ALBUM Formatstring: 'prefix string '%ALBUM%