How about something like this?:
title: clone-by-prefix
from: set/
to: set2/
From prefix: <$edit-text field="from"/>
To prefix: <$edit-text field="to"/>
<$button>
Clone all
<$list filter="[prefix{!!from}]" variable="old">
<$action-createtiddler $basetitle={{{ [<old>removeprefix{!!from}addprefix{!!to}] }}} $template=<<old>> />
</$list>
</$button>
-----------
!!! Tiddlers to clone
<<list-links [prefix{!!from}] >>
!!! Cloned tiddlers
<<list-links [prefix{!!to}] >>
It gives you edit boxes from the two prefixes and a button to clone them, as well as before and after lists of tiddlers.
Minor update for slightly prettier look:
CloneByPrefix.json (1.6 KB)