Orace tablespace extension operation
There shouldn't be any impact adding datafiles to an existing tablespace.

Easiest is to let oracle manage the files, make sure you have DB_CREATE_FILE_DEST set:

ALTER SYSTEM SET DB_CREATE_FILE_DEST = '%ORACLE_BASE%\oradata\';


Now the only thing to do if your existing datafiles are full or hitting the max autoextend limit is:

alter tablespace USERS add datafile;


where USERS is the name of the tablespace.