Bulk Edit Search & Replace expressions?

Sorry if it sounds crazy..

I'm trying to write a bulk search & replace to replace the tags column with #pages " Pages" (To look like 228 Pages" in the tags column that's otherwise empty). What I have is:
Regex: search field = tags
Search for: \*
Replace with: #pages " Pages"
Destination field: tags

It sees the tags field ok but just repeats it in the destination field. I've tried different replace with and nothing works. I've also tried in on books with a blank tags field.

Thanks