[Google App Engine] Key of type Long and setting value manually - what are the consequences?

Question

Google Workspace

Such is the question. GAE allows 4 types of keys (in JDO): String, Long (for orphans) and Key, Encoded String (for having a parent).

Moreover, it is everywhere said about the Long key that it is assigned by the system . But since the system assigns it crookedly (the numbers are out of order, the costs of a distributed architecture) - then I decided to assign it manually.

Everything seems to work, there are no problems. But there are doubts: the documentation does not say anywhere that a Long key can be assigned manually. And suddenly at one fine moment it will stop working (the system will assign itself, ignoring my keys).

In general, who can say for sure: can manually setting the value of a key of type Long lead to problems? Is it normal to set the values ​​of such keys manually