It is not usual English typographic practice to detach the period, and some other marks, from the word, though it certainly is, especially for some marks, in some other languages, French, for example. Though it is true that there are plenty of letterpress English books from the past that do detach some marks. But, assuming usual current English practice, I do wonder whether you really need to do this . . . you may have a special reason . . .

Well, I won't detach it to a degree similar to that in French. However, I do believe there is some room between a full space and a dot that forms a unit with the preceding latter, as seems to be the fashion in our poor day. My reason is aesthetic, or if you will it's a semantic sensibility. A period must render a rhythm to phrases, it must phrase them like a pianist does playing the score. To that end, it must not only be visible (I find even the visibility impaired when the dot seems a diacritic to an n or so), it must also be in some accord with the rhythm of the words. This doesn't call for a full blank space, but it does call for some air. Or so I feel. Cf. eg. attached beautiful setting.
Besides, while taking your assumption as a compliment, I usually work with german text.

illegal (minor issue)

Maybe not the best start to ask for help in a forum full of type designers.

You’re right. I should have said that I hope a change equally achieved by perfectly legal means present in a typesetting application would turn out to be legal in most cases, which is what I hoped to indicate by calling it a minor issue.
But I realise instead of hoping, assuming and indicating I better had looked it up in advance and made explicit that I will restrict my interventions to what’s permitted. (To pursue illegal intentions in a public forum signing with my real name would be a display of rather questionable wits indeed. And I assure you, not only am I willing to respect the license, I’m actually without capacity to change letter shapes or the like to the better. So, simply, I won’t.)
To the kerning matter: Now that I did a quick search, I find that e.g. Adobe’s Garamonds are even “licensed for modification” (cf. Additional License Rights).
I apologise, and hope the offence isn’t too great.

If this is Adobe Garamond, you can do the adjustments yourself, or pay Adobe or another type designer to do it. I would be happy to accomodate you. Drop me a mail if you need a quote.

Since you mention InDesign, Peter Kahrel's in-InDesign Kerning script comes to mind. (He has written more useful scripts.)

Also, have you tried using character-style GREP search/replace for this? I vaguely remember that someone had described how to use it for spacing punctuation marks.

Also, have you tried using character-style GREP search/replace for this? I vaguely remember that someone had described how to use it for spacing punctuation marks.

He mentioned GREP styles in the original post, so I guess he knows this technique. An article about this was posted by me on Typografie.info and there is something from Nina on Typophile.

That's it. Both of them.