Addnote was never intended to be a final solution.. someone needs to make a better note plugin with searching.
But you could do what you want by disabling the default addnote+viewnotes aliases and making your own.
Here is commandline options for addnote (see the -f option for specifying notefile name and path):
E:\MyDocs\Programming\CodeGear\FindAndRunRobot\Helpers>AddNote.exe --help
USAGE:
AddNote.exe [-o] [-r] [-m] [-p] [-d <string>] [-t <string>] [-f
<string>] [--] [--version] [-h]
Where:
-o, --open
open notefile after completion
-r, --report
report operation result with messagebox
-m, --bottom
add note to the bottom of the file
-p, --top
add note to the top of the file
-d <string>, --dateformat <string>
Format for time/date stamp (uses c strftime funciton formatting, see
readme)
-t <string>, --text <string>
Text to add (enclose in double quotes)
-f <string>, --file <string>
Filename to write to
--, --ignore_rest
Ignores the rest of the labeled arguments following this flag.
--version
Displays version information and exits.
-h, --help
Displays usage information and exits.
The addnote+viewnote aliases are in Aliases\Installed\Core_Aliases\Core-Helpers.alias
So easiest solution would be to copy that alias file to your Custom alias directory, rename it, then disable the normal core-helpers one and edit yours.