Remember previous value of the field

Remembering until when? During the update and the save operation (Templates, OnSaving-Script, Process gen.conditions, ...) you can access the old-value using the $-notation.

$UID_Department[o]$

You can enable History Features (Common\ProcessState\PropertyLog) without an additional database.

However, the values are only stored for a period of <LifeTime>, regardless of how often they have been changed.

If you only need the previous value for a single field at any time, you might want to save the old value to a separate field when it gets updated (in the column template or format script).

For how long the old value is available? Is this lifetime value configurable?

Yes it is. Find more in the Configuration Guid, Section Tracking changes with process monitoring https://support.oneidentity.com/technical-documents/identity-manager/9.2.1/configuration-guide/66#TOPIC-2204243

Logging data changes https://support.oneidentity.com/technical-documents/identity-manager/9.2.1/configuration-guide/66#TOPIC-2204245

Archiving and deleting records https://support.oneidentity.com/technical-documents/identity-manager/9.2.1/configuration-guide/68#TOPIC-2204254