Stardocks licensing/activation process is pretty secure from what I've seen. Is it correct that before a second computer could be activated with the same license key, that previously activated license would need to be released/deactivated? So no need to check if any specific license is "valid" because one way or the other the license is made 1:1 for a single device and is either in an activated or ready-to-activate state. It is nice of Stardock to create that process to migrate the license though.
Very unethical to attempted to hijack a ride out through WinExplorer when you've previously attempted through Fences.exe unsuccessfully. The only reason fences runs in WinExplorer is to do the job it's purchased to do. That decision specifically seems like a huge legal risk for less than $10 license. EULA's aside, the only thing I've ever seen attempting to hijack a way out through explorer.exe like this is Fences and actual malware/viruses.
You should also consider being more transparent with users when giving them the HKCU "fix" to stop the update checks and phoning home. The "fix" doesn't stop the phoning home, it just stops reporting that it has. Tricky! I'm sure Stardock knows the intent of the users on these forums requesting this solution is not so much to stop the nags, but to polietly ask you, as customers, to stop you from phoning home from a program that has been purchased, registered, and fully activated.