Section 179 - using car at lower percentage than previous years

Hello. I am filing a 2019 tax return for my S Corp. I have two cars titled and registered as personal (not business), one car is mainly used for business related trips. It was financed until mid 2019 when I paid it off, the loan was under my name, not the company. 

I am at Deductions - Business Asset Summary (Form 4562). My CPA listed that car as an asset with 100% business usage on previous tax returns. I used the car more like 80-90% for business related trips, but I want to add it as 70% just in case. If I change the percentage, it changes the Depreciation and AMT numbers. Should I manually change the numbers for previous years or is it okay to put in amounts different than prior years?