That will only give Everyone: 'Read & Execute', 'List folder contents', 'Read', 'Write'. They must have the Modify rights too.
AccessControl::GrantOnFile "$INSTDIR\cactid\" "Everyone" "GenericRead + GenericWrite + GenericExecute + AppendData"
Looking through static const char * g_filePermissionNames[] in accesscontrol.c, I can see all the various names, but apparently the AppendData doesn't do what it should.
I realize I could use the microsoft xcalcs tool in a seperate script, but I'd rather keep as much of the scripting inside the NSIS installer as possible.
How can I accomplish this?