Need help in updating property-values

I had to do an update on a class-property and all its instantiated document.properties.
The property is a static-list and multiselectable.

Example:

Class:
I had to do an update on a class-property (e.g. XY-OrganizationClass - (organunit: Static List)) and all its instantiated document-properties.
The property is a static-list and multiselectable.

Example:

Class:
old values: [100,200,300]
new values: [100-120,200-120,300-120]

Document-instances:
old values: [100|200], [100], …
new values: [100-120|200-120], [100-120], …

How can i do that?

Thanks in advance

I have solved this by updating the underlying database