First, Tell everyone you know who owns a Mac, including Apple employees... Mac Migration and Time Machine DO NOT WORK properly with Adobe program activations due to hidden registration files that are not included when Migration or Time Machine make their copies
Error 150:30 License fix https://helpx.adobe.com/x-productkb/global/error-licensing-stopped-mac-os.html may help
When you have a non-functioning computer and can't deactivate
Be sure to ONLY ask for activation support to adjust your activation count
Serial number and activation support (non-Cloud) https://forums.adobe.com/thread/2041990
CS6 and earlier programs have not been tested and will not be updated to run on Mac El Capitan
-which means that you try to use CS6 and earlier at YOUR risk of having problems
-you may get CS6 and earlier programs to install and run, or you may not (some do, some don't)
Install CS5 on Mac 10.11 https://forums.adobe.com/thread/2003455 may help (also for other than CS5)
-also a TEMPORARY security change https://forums.adobe.com/thread/2039319
-and more on gatekeeper https://support.apple.com/en-au/HT202491
-and more help in http://helpx.adobe.com/creative-suite/kb/invalid-serial-number-cs4.html
Thank you John for the thorough and thoughtful reply.
I could go into a long diatribe about how much I've paid Adobe since PS v2, and how their tech support should have been able at a keystroke to supply the cogent response you did. But I won't
The escalation tech told me directly that Adobe COULD NOT deactivate my dead install...that only I could...even though you and I know better. Awful customer support seems to be the norm these days.
At least the suggestion [after two hours of fruitless chat] that I go to this forum would have helped more than I expected.
Anticipating the worst, I simply activated another copy of LR prior to your post and all is well. Suppose this suits Adobe just fine. [$core one more for awful customer support.]
I notice LR is now branded with the 'CC' moniker, so ahead of the subscription apocalypse my next steps will be to start learning ACDSee again. I see it's matured quite profoundly, and with none of the Adobe licensing nightmares.
Best to all,