As the subject says, Can I change the file-system of a usb (or say any drive) from it's current partition like :- ext4 to a different partition like:- ext2/fat/ext3/ntfs file-system without loosing the data in the drive and without taking backup.
From File system Wiki
So it seems it is not Back-Convert-Compatible and Converting from ext4 to NTFS will require Formatting , since they are totally different File-systems , also holds true for ext4 to Fatxx format .That means without data loss
ext2 >> ext3 possible
ext3 >>ext4 possible
ext3 & ext4 >> btrfs possible
ext4 >> ntfs not possible w/o Format
ntfs >> extX not possible w/o format
Please refer this question on superuser also.
The simple answer is that it depends on which filesystem you are "converting" from & to. There needs to be a specific program to convert it for you.
For example, a FAT16 or FAT32 filesystem on Windows can be converted to NTFS via the Windows "convert" command. However, generally you cannot convert filesystems.
1 other option that may work though: Ext4 filesystems can often (but not always) be mounted as ext3 or ext2. Similarly, Ext3 filesystems can often be mounted as ext2. e.g., on windows, I mount Ext3 & Ext4 filesystems using the ext2 driver ext2fsd: