By specifying *REPLACE, you essentially clear the member. The copied records are the only records in the member when the operation completes. You must have authority to clear the member in order to specify MBROPT(*REPLACE).
For copy commands other than the CPYFRMQRYF command, when you specify *REPLACE, copy command processing fails if the from-file does not contain any records. When you specify *REPLACE on the CPYFRMQRYF command, the to-file member will be cleared even if the open query file contains no records.
*REPLACE is the default value for the CPYSRCF command. All other copy commands have the default value of *NONE; however, *NONE is valid only for copying to a device file.