How you load the executable file is dependent on what stage you are at in the design/debug process.
At the design level, you can use Data2MEM at the command line to modify the BRAM content with a new executable file. You can also mark the SW Project in XPS to initialize BRAM (this assumes that the full executable will be located in the BRAM, including the BSS file, if not, XPS will issue an error).
After downloading the bitstream to the FPGA, you can use iMPACT to load a new configuration bitstream as follows:
1. Right-click on the FPGA target in iMPACT.
2. Assign the system BMM file (make sure that the BMM file is the back-annotated file; use the system_bd.bmm file located in /Implementation in the XPS project directory).
3. Assign the new executable file. After reconfiguring the FPGA, iMPACT will load the new executable to the BRAM.
At the debug stage, you can use XMD commands to load a new executable to the FPGA BRAM as follows:
1. Launch XMD, then use the "dow" command to load the new executable.
2. You can also use the GNU Debugger to load a new executable to the BRAM.
3. If you already have an open debug session from GDB, make sure to reset the target from XMD (by typing the RST command in the XMD Shell0 before loading the new executable from GDB).