I have a presentation created in a well known presentation program.  It
was created with a font I don't have on my computer.  It imports into
Impress very cleanly, including animations.  However, I don't have the
same font as the original author.  Impress picks a similar font that is
just slightly larger than the original.  This causes some bothersome
visual formatting errors.

I want to change the font definitions on all the slides all at once.
The same font is used through out but is larger for the headings and
smaller for some of the minor bullet points.

1. How do I select all of the text on every slide all at once?

2. Once I have the text selected, can I do a relative shift about 5
points down on all of the text?  For example, I want the 20 point text
to drop to 15 and the 18 point text down to 12.

I have not found a way to do this from within the application.  Having
converted it to an .odp file, maybe some text manipulation of the XML is
in order but I have not found a tool for that either.

Any thoughts?

Alan