JPP,
Briefly (as I am still on hols)
Existing certs... I have only seen mails relating to test certs (not sure if this can be optionally disabled.... Letsencrypt decided to do this, not me or dehydrated)
If your originals are renewed correctly the old ones should become irrelevant surely ? If they are updated correctly by dehydrated the hook script (should) take care of paths.
Curl.... Hook script only works after the certs are generated, not before, so you'd either need a 'pre' hook or if you think ENV vars them something in cron or the script itself.
Either way it a bodge and not an elegant 'SME' type solution. I'll look further next week and possibly speak to the developer.
Give me a few days.
B. Rgds
JC
PS might it be better to add this contrib to CVS so it can be bugged rather than discussed here on the foros (I tend to miss a lot here) It can always be obsoleted if it gets built in to SME ?