Select package version in package_config?

[Steffen Grunewald]

On Wed, Jan 22, 2014 at 01:07:56PM +0100, Thomas Lange wrote:
> >>>>> On Mon, 20 Jan 2014 13:03:42 +0100, Steffen Grunewald <Steffen.Grunewald at aei.mpg.de> said:
> 
>     > Until the reason of the grub problem has been identified, I'd like
>     > to set the version for all 5 grub* packages to 1.99-27+deb7u2 
>     > explicitly (or, to cover the chance of the Wheezy package being
>     > updated again, to << 2.0) - is this possible within FAI?
> You can do this with apt pinning, but don't aks me about the details.
> It's also possible to say packagename/distribution (like
> grub-pc/wheezy) in the package_config files.

I've just come across another quirk which needs unconventional handling:
it's the hdf5 package set which comes without libhdf5-serial-dev.
The accepted workaround is to install that package from a Squeeze repo,
put it on hold, and install a tweaked (build -9.1) version of Wheezy's
libhdf5-7 over it.

I presume that the most adequate way to represent this in FAI would be
a hook, right?
When would this best happen, just after unpacking the base package? 
Would FAI obey the "hold" setting?

Thanks,
- S