I've been investigating how to set a password validation string but in the process have a very unusual behaviour. I am using AEM 6.2.
Starting with a freshly-installed system at http://localhost:4502/system/console/configMgr, I search for 'Apache Jackrabbit Oak AuthorizableActionProvider', click on that name to open the configuration to open the configuration dialog, then click 'Save' from the buttons in bottom-right corner of the dialog. Do not make any configuration changes, just open the dialog and click 'Save'.
There is a message at the top of the window after this: 'Configuration Admin Service is running.'
There are some known issues in AEM 6.2 GA instance. You can see issues notes in 6.2 SP1 release notes such as
Changing Oak-related OSGI configuration makes the AEM instance dysfunctional. GRANITE-11906
Fixed issues around instances becoming non-responsive when Sling Resource Resolver Factory is updated. GRANITE-13126
I suggest you update your instance to the latest SP+CFP which would be SP1 + CFP14 and re-try to see if you face any issues. I've just performed a quick test on mine SP1+CFP14 instance and didn't face any issues.
when you re-configure Oak services, typically a lot of AEM is restarted; that's because this service restarts, but before that OSGI shuts down all depending services, the services these depending services depend an so on. In most cases that's comparable to a complete restart of AEM.
When testing this, you should validate in your log file when the services restart is over, and then everything should be fine again.
These are my findings from trying out the suggestions. This was my first upgrade so I read the documentation carefully and did a number of tests. Since SP1 requires Hotfix 12785, and CFP15 is optional after SP1, I tried the following combinations:
HF12785 on its own: did not fix the problem (as expected)
SP1 (including HF12785): fixed the problem
SP1+CFP15: fixed the problem
All the answers above were helpful but I have chosen aneeta45259594's detailed answer as the correct one. Thank you!