You cannot load a registry file that is already loaded.
You cannot load a registry file into the HKLM hive. Self loaded hives will be loaded into the correct hive by default.
Start by reading the help for the various commands.
reg load /?
reg load hku\usertest C:\users\TestUser\NTUSER.DAT
You must be running as an elevated admin to use this command.
I do not believe that SetAcl requires the hive to be loaded. Skip the load and try from an elevated prompt to just use the SetAcl command.
For assistance using security command line utilities post in the correct forum. The Security forum is the correct forum.
Your issue has nothing to do with batch files.
\_(ツ)_/