Model Refresh

Hi,
I am struggling to understand how the Refresh module works. As per my understanding and documentation, the model refresh takes a base model, updates the range for hyperparameters from the base model and then updates the model with following criteria:
1) Stable baseline compared to the the base model
2) Media spend changes in the new period are reflected in the refreshed model which is the objective

However, I am unable to wrap my head around on how the above criteria is being handled in the code (pardon my R illiteracy). Further, with only a few data points added to refresh the model, how will the coefficients change to reflect the changes happening in new period added as the weight would be too less for a few data points.

Do we make some changes in the objective function to achieve the desired results. If yes, which part of the code handles this?

Please help here so that I can understand how the refresh module works to reflect the changes in the new period.