modifying interval partitions

I have Oracle 19C RAC environment on Linux with DB 19.3 installed.

I have a table that is partitioned by RANGE-INTERVAL partitioing on monthly basis, as follows:

 PARTITION BY RANGE ("DATABASE_DATE") INTERVAL (NUMTOYMINTERVAL(1,'MONTH'));

i want to modify this partition to be on weekly basis i know the below:

1- ALTER TABLE XSET INTERVAL (NUMTODSINTERVAL(7,'DAY') );  would this do the job, i know that with this command only new records will have the new interval partitions and the old data would still be in monthly partitions. / should i run gather stats or update indexes after this command

2- what is the impact of running such command on a big table that is always online and heavily accessed, would there be any impact on the table while the alter is run.