I'd like to second this request. I know you've suggested using an external app for creating sequences before, but it'd be much more elegant and clean to be able to execute a sequence of find/replace snapshots as a single action from within PM so that I can rewrite image captions more efficiently.
One such example I'd like to create in a single action sequence is:
Find/replace copyright statement in caption
Find/replace byline statement in caption
Find/replace or add keywords
Apply specific IPTC/Metadata config
to modify IPTC different destinations, often as a routine numerous times on a single job as batches of photos get sent out.
If I could create sequences which carry out a set of specified find/replace action/s and apply specified metadata preset/s, that'd be a big efficiency for me.