I have dataset of a company with 2014 data with 15 variables then 2018 data with same 15 variables.I want to combine both the datasets however the meaning of 1 variable has changed meaning that variable no longer has same significance in both datasets. How to deal with this variable? whats the best approach for building machine learning model in this case? Also, importance of the variable according to model summary is fairly good in both the datasets. I am building the GBM model here.