Snaphot for backup changing files with rsync?

1. 
   

   With rsync, is it acceptable to modify some files in a file system, while backing up the file system?

   
   

   If yes, is it necessary to take a snapshot before backup, and do an incremental backup after finishing modifying the files to keep the backup and the source the same?

   
   


2. 
   

   Which is better:

   
   
   
   
   • wait and not change any files during a full backup, or
   
   
   • modify some files during a full backup and then do a incremental backup after modifying the files?
   
   
   
   

   I want to change some files of a large file system while backing it up, because I heard that incremental backup will be much faster than a full backup. Is that correct? So I can wait shorter for backing up?

   
   


3. How do we do snapshot with rsync?