Hi
The Calibre editor and Sigil offer to store your "saved searches". I know there are some small differences between them about the regex flavor being supported but I am unable to tell precisely which does what.
On the other hand there are also excellent sites for training and testing purposes like
https://regex101.com/.
Is the latter compatible with either Sigil or Calibre? It offers (among several other flavors) a PCRE option.