User defined data pattern during load phase

[gunnerVivek]

I wanted to load test hbase through YCSB. But we have a requirement to test performance of HBase after specifying region splits manually. Thus we need to be able to create a user defined pattern for the row_keys, as suggested in the standard HBase guide where they prefix every row_key with user followed by a number. We want to do something similar, so my question is can we ask YCSB to insert data that follows a certain pattern during load phase? Or will it only insert randomly generated data?