**In my opinion**, doing it in the way you suggested (mounting, doing workarounds for updating and configuring, etc.) **presents more challenges than actual solutions**. Sure, it may be fun to do it your way if you're interested, but the best and easiest way may be the one you're avoiding.

If I were to do it, I would get a Pi and do what I have to do on it, then make an image of its SD card. Then, use that image on my other Pis since that image is already configured.

*I'll assume you'll use Raspbian.*

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Steps if you **do** tinker with your Pi:

1. Download and install fresh OS of your choice
2. Plug in Ethernet cable/connect to WiFi
 - Possibly do a LAN scan if you don't know your Pi's IP addres
3. Do stuff via SSH
 - `apt-get update -y && apt-get upgrade` to update packages
 - Your personal configuration needs
4. Make an image, then use that image for other Pis.

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Steps if you **don't** tinker with your Pi (and you're not familiar with [building an OS image from scratch][1]):

1. Download fresh OS
2. Mount it using instructions from http://raspberrypi.stackexchange.com/a/13138/24224 (you also have to consider what OS you have since some have different FS layouts)
 - Have a calculator ready.
3. Find the `deb` file for **each and every package** you want to update, plus **their dependencies**, plus **those dependencies' dependencies**, plus those **dependencies' dependencies' dependencies**. `apt-offline` is a hassle. Refer to [this link][2]
 - Then find a way to install all of those packages without using/tinkering with your Pi. `apt-get` won't work on offline OSes. `deb` [file details here][3]. Good luck.
4. Update the Pi kernels and low-level stuff using [Hexxeh's tool][4]
5. Configure to your requirements
6. Write modified image to your Pis' SD cards.

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I don't see any benefit in not tinkering with your Pi. It's not like you have to tinker with each and every Pi you encounter.

Cut yourself some slack and tinker with your Pi. You only have to do it once.


 [1]: https://www.raspberrypi.org/forums/viewtopic.php?p=343580#p343580
 [2]: https://www.raspberrypi.org/forums/viewtopic.php?f=31&t=14737
 [3]: http://askubuntu.com/a/110992/391854
 [4]: https://github.com/Hexxeh/rpi-update#root_path-and-boot_path