“Template Changer” is the 6th most popular extension for Writer, as ranked by “likes:”
http://extensions.libreoffice.org/extension-center?getCategories=Writer_Extension&getCompatibility=any
A “medium” priority core feature request has been made, but I would guess many users are impacted by this change and will need to downgrade (as I have).
https://bugs.freedesktop.org/show_bug.cgi?id=60660
Update 2013-06-14
There’s now a beta release template-changer-1.2.7b.oxt for LibreOffice 4.
Feel free to test Template Changer 1.2.7b.
Bug 60592 - Template Changer: Can no longer assign document to different template, extension will not work · Comment #8 (with download link):
László Németh 2013-06-14:
“This beta release contains the necessary fixes for LibreOffice 4.0.
The menus have been moved to File » Send …”
Test: LibreOffice 4.0.4.2 RC
Update 2014-07-20
There’s an updated version of Template Changer:
template-changer-1.2.7c.oxt
psmits 2014-07-18:
“New version of Template Changer that
resides under Files/Templates.”
Wahey!! (Or is it “w00t!”? So hard to know!) Just tested on 4.0.3.3 (OS = Linux Mint 13/Xfce), and it works great! Wonderful stuff. And interesting to see the fix comes from the Linux Libertine Graphite version contributor. He’s adding serious value, isn’t he! Thanks for posting this, @manj_k.
[ @Thoms ]
I’m missing your question.
[ @all ]
Please read also these addtional bug reports with regard to
“Template Changer”:
→ Bug 60592 - Template Changer: Can no longer assign document to different template, extension will not work
(especially comment #6 by A. Sch., the maintainer of the extension)
→ Bug 50699 - Template Changer: Allow ability to change a document’s associated template.
"Partial workaround" for the current version LibreOffice 4.0.1 (Writer)
(a simplified example)
(1)
Open the “Styles and Formatting” window
Select the rightmost icon
Select “Load Styles…”
(2)
Select your desired template (or "Frome File…)
Select/deselect 
/☐ Text/Frame/Pages/Numbering/Overwrite
(3)
Click “OK”
You caught me! I knew it wasn’t a question 
Appreciate the clarification, as the process in the bug report wasn’t so clear. Thanks!!
What about the Calc? I can’t find Load Styles option?
@froz – Template Changer is a Writer extension.
I’ve added the TemplateChanger Help item to my answer.
"You can assign a document template to one or more text documents by using the TemplateChanger extension. […]
File - Templates - Assing template (current document) (LibreOffice Writer only)."
An additional note for others: the process outlined above does not fully replicate the functionality of the TemplateChanger extension. It will load styles from a template. In my experience, it will not update the styles in a document to the formatting used in a template file.
@manj_k - Thanks for “Load Styles” technique - works a treat on 4.0.2.2! (Even with @Thoms caveat in mind…)
