When booting using Target Disk Mode, all iCloud, Adobe, Microsoft credentials are lost. Is there a way to keep the credentials?
Here's some clarity for anyone looking. The root cause of the sign in when switching the host is that programs often store their license information x'ord (or otherwise encrypted with) a hash of the host hardware. This means that, when the hardware changes, the previously stored configuration is unrecoverable. I've tried spoofing the MAC address, but all programs I test seem to do a deeper hash using the hardware (e.g. system_profiler). I've found a number of workarounds, though:


Stop using apps from the App Store. While the app store uses this hardware hash technique, many indie programs don't. For those, buying directly works (e.g. Moom)
Where possible store the license information in an un-hashed version. For example, Sublime Text supports this by editing the license file (see https://forum.sublimetext.com/t/st3-license-not-syncing/11738)
I've found that the iCloud sign in behavior stopped when I created my own keychain (not the default login) and set it as default. Not using an App Store apps, and using this new default keychain, I get no prompts to log into my iCloud account on start up


After this, some programs that are still offensive are: Office 365, Creative Cloud, and Mathematica. I ended up finally ditching Creative Cloud - I've long switched to other tools, so the one part that I still use (Font syncing), I just downloaded all the fonts locally.

Overall this is pretty good now. After switching hosts, I get zero dialogs to log in. All my main flows work (Thunderbird, terminal, Sublime). Occasionally I have to log in, but much less of an issue than before.

Hope this helps.