Freeze the last year data in Power Bi in Analytics model

HI,

Can anyone please help meto solve this issue?

I have the 2017 data in my model, so next year 2018 i am going to change some data like relationship and 2017 data might ne change.

so i want to be save the data and reports in the memory  in end  of the year or data should be saved in some place to extarct when we need the data for 2017 in 2018 year, it will  pull the data from 2017 data set from saved data in memory.

we should not use any database.

Please get back to me,if you dont understand this issue.

Thanks,

Kapil