Is MAGI limit impose to only current year ROTH IRA contribution?

If  MAGI exceed the income limit for ROTH IRA contribution in 2019 and beyond years, does this effect the previous years ROTH IRA balance, contributions, or earnings?

 

For example, I have a ROTH IRA account since 2015. In 2019 and subsequent year, I can't make any contribution due to high MAGI. Can I still keep my 2015-2018 as is and let it grow? Or do I need to do any adjustment to 2015-2018 contribution or earning?

 

Also, any future years with MAGI falls within the income limit, I can contribute to ROTH IRA for that year again correct?