True Dev unlock is simple, you bought an account from Microsoft, and used their official software to perform the unlock to let you side load apps. With the legit Chevron lock being discounted, its the only way we know of now.
Levels of unlock (as far as I understand them)
From lowest to highest levels:
Dev unlock (Chevron, official Microsoft)
Interop unlock (modding dev settings to sideload an unlimited number of apps)
Root/policy unlock (You get this by installing
WP7 Root Tools on a stock rom)
Full unlock (Flash an unlocked rom).
The official WP7 Root Tools website
has a great writeup on what all the different unlocks do.
As far as manually doing interop unlock on the Verizon Trophy, to do it, you need to be running the Mango v1 rom ("RUU_Spark_W_S_VERIZON_WWE_2.01.605.04_2K_new_partition_RELEASE" or the
2.01.605.04 drivers). If you have newer drivers installed then that such as the newest 2.
04.605.04, or the 2.01.605.10 drivers, using the older methods to perform interop unlock won't work.
I think there might be an newer method, but I never got it working in my test.
As far as applying the tethering policies and registry settings, the only way to really do it is to use the Mango v1 rom as your base, then apply registry changes settings after interop unlock with a registry editor. IF you use Zune update and install newer drivers, those changes are gone, and the Mango v3 drivers (2.
04.605.04 that come with the official driver) totally do not work using this method.
I am exploring the option of using a driver from the HTC Titian, but the long way of putting that onto a stock rom would require somehow getting Yuki certificate installed on a stock phone (might be possible now or soon?), then creating a custom.cab to replace the wireless driver. That's the path I'd love to see.