I would never suggest the shortcut of modifying the rear bulk head to enable the oil filters to be changed with out removing the pack.
Pack removal is a vital part of the servicing and maintanence programme.
It's only when the pack is removed can you check all the clips, hoses and feed lines. The first you would notice something is wrong is when something breaks or over heats.
Pack removal isn't hard as long as you have the right lifting frame.
I'm speaking through personal experience as we removed my pack at War and Peace after suffering oil loss on a massive scale.
If I had practiced what I am now preaching - I could have spotted the issue long before it bacame an issue.
Armoured vehicles need their packs lifted and any shortcuts taken on this issue will lead to certain failure at some point.
If you can get one, a spare pack makes a lot of sense. This enables you to change the pack over and then you can service the removed pack without losing the use of the vehicle.
Markheliops