It is necessary to set initial value of the internal variable and later let the operator change and keep its changes. I see the manual Variable -> Internal variable -> Remanence.

Off: When starting Runtime, the alternate value of the variable or an empty string for string variables is used as the current value
Initial value: The current value is the value entered in the property “Initial value”
Remanent: The last value of the variable is used as the current value when restarting the Runtime.

In result:
Intial value: Сan set initial value, but can't keep its changes.
Remanent: Сan't set initial value, but can keep its changes.
Is there no way both initialize and keep changes of the value of the internal variable?

BR, Andrey