Question: My problem is every time after changing the Liferay `portal-properties` (and this is frequent especially at beginning of a new portal project) I need to restart the whole portal.

Some properties I can set over hook and these values will be changed after redeployment. Also that must be possible to change most portal properties at run time. 

However, do you know some approach to reflect changes in `portal-ext.properties` without restarting Liferay portal?

Answer: 
This has also been asked in Liferay forums:

<https://www.liferay.com/community/forums/-/message_boards/message/800954>

But I am afraid that most properties are only read once during portal startup.
Usually, the use of a properties file as in this case has this drawback.

There's even an issue open at Liferay about this, but is still unresolved:

<http://issues.liferay.com/browse/LEP-5579>
If you create a hook to override portal properties, you will be able to change properties with just deploying the hook without restarting the Portal. 

Be aware that you cannot modify all properties with a hook. For a list of the ones that you can modify, check out: <https://docs.liferay.com/portal/6.2/definitions/>.