|As long as you have: |
Tools | Options | Message Text Quoting | Quote text when replying
checked, your reply will automatically contain the quoted text.
If you want to only comment on a section in your reply, simply hilight that section in the original message before hitting reply. (Check out this article for more information on this topic).
I think I understand what is being requested here, the requestor is not wanting Poco to automatically quote the message he is replying to but only to do so when he requests it. Although this could be done via a script I would not recommend it as it would be tricky to implement (you would need to copy the prior message headers to ensure proper threading) and you would lose the automatic setting of the reply status (or the automatic removal of it if you elect to cancel the message).
A better option may be on the horizon, if Slaven adds the ability to allow scripts to run against the compose window plus other suggestions I've made to him then this feature could be scripted directly to the compose window.