There are three ways to do this but you can't "tag" positions on the page.
The first way is quick as long as you have all the text frames connected, so if you select all the text it selects all the text in the document.
Then use File>Export and choose RTF.
The text can now be opened in MS Word and the changes made. The RTF retains the Styles you've made in InDesign. So reimporting the text is easy enough.
The second way is by way of XML:
You need to create a bunch of tags for everything in your document. (Window>Tags)
So you need to build a structure. Create tag names like H1 (for the 1st heading) H2 (for the second type of heading etc.) Set P tags for body text. Table tag for tables, IMG tag for images etc. (you can name your tags anything you want, just make sure they are consistent).
You need to apply each tag in the order it is in the document, i.e., start at the first page, select the first paragraph style and apply the correct tag. Move to the next paragraph and apply the tag.
You would also need to tag things like Italics, Bold, Bold Italic etc. that are character styles.
Ok, it sounds like a lot of work! But once it's done it's done and it's easy for you export the XML out so anyone can edit between the tags.
Once you get the file back you can import the XML file back in and everything is just as you had it.
The third way is probably the easiest way, but it's also a bit expensive. It's by way of InDesigns sister program InCopy. You create assignments that can exported to an InCopy workflow. The assignments are worked on in InCopy. When you recieve them you import the assignments and whatever text was changed in InCopy is updated automatically in Indesign. I'll be the first to admit that this has a learning curve.
To be honest the XML workflow and the InCopy workflow have learning curves for everyone invovled.
The RTF workflow is pretty straightforward, as long as people don't start putting in their own styles and messing with the layout in MS Word, it all comes across nicely.
If you're interested in the XML workflow you chould check out "A Designer's Guide to Adobe InDesign and XML".
If you're interested in the InCopy workflow you should visit
for guidance.
Oh wait, there's a 4th way! In InDesign CS4 you can have "Conditional Text" which a bit is written about here