Package Devel - altering other packages

[Tony Atkinson]

Hello all,
I think I'm sending this to the right place, but apologies if this is
the wrong list

I'm toying with producing a software package (initially for Ubuntu, as
that's my main OS - but potentially for all distros)

Briefly, this package will allow the user to setup an encrypted VPN
(using iPredator or similar service) and configure it to proxy certain
traffic

Currently, I can do selective proxying based on:
- Port ranges (using iptables and routing rules)
- www domain names (using squid)
- Any traffic from select applications (jailing a process so the proxy
interface is the only one it can see)

This package is not original software, in fact it mostly just tweaks the
configuration of other software packages

Are there any guidelines for altering other software's configuration?

I'm cautious of the fact that any user may or may not have (for example)
squid installed, and how can I setup my software (which alters the squid
config) without breaking their setup

Many thanks

-- 
Tony Atkinson
Email: tatkinson321 at googlemail.com
PGP: F2B9184B
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