i would like to modify the font used by the Text Body style when i export a file to odt.
The easiest way for you to achieve what you want is to use the FORK of the ODT exporter (See Project Summary (OpenDocument Text Exporter for Emacs’ Org Mode)).
The keyword you are looking for is#+ODT_EXTRA_STYLES
(See Applying custom styles (OpenDocument Text Exporter for Emacs’ Org Mode))
Here is a sample snippet and the corresponding output.
In the snippet,
- The
Text Body
style is modified to use Courier New
- The
OrgVerse
paragaph style--this is the style used by the verse block--is configured to use Comic Sans
#+odt_preferred_output_format: pdf
#+odt_extra_styles: <style:style style:name="Text_20_body" style:display-name="Text body" style:family="paragraph" style:parent-style-name="Standard" style:class="text">
#+odt_extra_styles: <style:paragraph-properties fo:margin-top="0cm" fo:margin-bottom="0.212cm" loext:contextual-spacing="false">
#+odt_extra_styles: <style:tab-stops/>
#+odt_extra_styles: </style:paragraph-properties>
#+odt_extra_styles: <style:text-properties style:font-name="Courier New1" fo:font-family="'Courier New'" style:font-style-name="Regular" style:font-family-generic="modern" style:font-pitch="fixed" fo:font-size="16pt"/>
#+odt_extra_styles: </style:style>
#+odt_extra_styles: <style:style style:name="OrgVerse" style:family="paragraph" style:parent-style-name="Preformatted_20_Text" style:master-page-name="">
#+odt_extra_styles: <loext:graphic-properties draw:fill="none" draw:fill-color="#729fcf"/>
#+odt_extra_styles: <style:paragraph-properties fo:margin-left="0.499cm" fo:margin-right="0cm" fo:text-indent="0cm" style:auto-text-indent="false" style:page-number="auto" fo:background-color="transparent" fo:padding="0cm" fo:border="none" style:shadow="none">
#+odt_extra_styles: <style:tab-stops>
#+odt_extra_styles: <style:tab-stop style:position="1.0cm"/>
#+odt_extra_styles: </style:tab-stops>
#+odt_extra_styles: </style:paragraph-properties>
#+odt_extra_styles: <style:text-properties style:font-name="Comic Sans MS" fo:font-family="'Comic Sans MS'" style:font-style-name="Regular" style:font-family-generic="script" style:font-pitch="variable" fo:font-size="12pt"/>
#+odt_extra_styles: </style:style>
This is a poem by Rudyard Kipling
#+begin_verse
If you can keep your head when all about you
Are losing theirs and blaming it on you,
If you can trust yourself when all men doubt you,
But make allowance for their doubting too;
If you can wait and not be tired by waiting,
Or being lied about, don’t deal in lies,
Or being hated, don’t give way to hating,
And yet don’t look too good, nor talk too wise:
#+end_verse
(In the above verse block, the indented line uses a SINGLE TAB)

Btw, as you might have guessed, the user manual for the FORKED VERSION of ODT exporter is Top (OpenDocument Text Exporter for Emacs’ Org Mode).