[plug] updating packages (Debian) from later sources

[Denis Brown]

I guess that's a confusing subject line so to explain...   If I install a
programme from source, say Apache2, then it lives predominantly in
/usr/local/apache2 and subdirectories.   If I subsequently want to delete
it then I can probably do so without creating system mayhem by simply
deleting all of the /usr/local/apache2 directory and its
subdirectories.   Something like Apache should be non-critical for the
health of the overal Linux system.

Now let's say I have perl installed, version 5.6.1.whatever from the
Debian packages list.   For whatever reason I would like to update it to
version 5.8.whatever from source.   I am confident that I can get the
source, compile and install it.  Perl, I imagine to be a bit more
central to OS health, being necessary for running perl scripts for
example!  The questions I have are these:

1) should I remove the "old" perl package eg. using dpkg or the apt
system, before I install my new perl?
2) is this upgrade likely to break anything depending upon perl as
installed by Debian?  Special symlinks for example?
3) if for some reason I wanted to subsequently retreat back to the Debian
perl package how would I uninstall the new version? Simply delete the
directory(ies?) where the new perl resides?
4) do I need to "inform" the apt system about the changes so that if in
the future an official Debian updated perl package becomes available, I
can avoid its automatic "update" via the usual apt-get update;apt-get
upgrade route?
5) if I install the new perl under, for instance, perl5.8, then I suppose
I can point to it via etc/alternatives?

I imagine that the same queries would arise for RH people using their rpm
system so a response pointing to a general tutorial on this topic --
clean replacement of pre-pakaged programmes by install-from-source -- is
likely to be more widely appreciated.

The direct motivation by the way is that I'd like to experiment with
mod_perl and while I can play around with it using the existing
Debian-packaged perl I may as well play with the latest stable perl and
apache from sources :-)

Thanks in advance,
Denis