Analysis Services partitions have to be refreshed as a unit, meaning that you cannot selectively update certain rows of a partition. If your large cube only has one partition for a given table/entity, your first step should be to create partitions so that you can perform an incremental refresh of certain partitions in the future.
The "LoadedOn" date you mention might be a good attribute to use to identify which partitions have to be refreshed, if you want to do that programmatically...but it's not a good partition key. You'll need a date that doesn't change after the initial insert as a partition key (i.e. to determine what partition the data needs to go to.
Here's a reference you can use to get started: https://learn.microsoft.com/en-us/analysis-services/tabular-models/partitions-ssas-tabular?view=asallproducts-allversions