Once you have changed the block size at the cluster level, whatever files you put or copy to hdfs will have the new default block size of 256 MB
Unfortunately, apart from DISTCP you have the usual -put and -get HDFS commands
My default blocksize is 128MB see attached screenshot 128MB.JPG
Created a file test_128MB.txt
$ vi test_128MB.txt
Uploaded a 128 MB files to HDFS
$ hdfs dfs -put test_128MB.txt /user/sheltong
see attached screenshot 128MB.JPG notice the block size
I then copied the same file back to the local filesystem,
$ hdfs dfs -get /user/sheltong/test_128MB.txt /tmp/test_128MB_2.txt
The using the -D option to define a new blocksize of 256 MB
$ hdfs dfs -D dfs.blocksize=268435456 -put test_128MB_2.txt /user/sheltong
See screenshot 256MB.JPG, technically its possible if you have a few files but you should remember the test_128MB.txt and test_128MB_2.txt are the same files of 128MB, so changing the blocksize of an existing files with try to fit a 128bock in a 256 MB block leading to wastage of space of the other 128MB, hence the reason it will ONLY apply to new files.
Hope that gives you a better understanding
