Starting an InputScript in a .bat file: Is it possible to call up an InputScript from a .bat file?

Yes it is. Example:

Start "no title" "C:\Program Files (x86)\SAP\FrontEnd\SAPgui\guixt.exe" "input=ok:/oMM02,process=extern01.txt"

(all in one line, /o is the letter o, not zero)

This will call transaction MM02 and process the InputScript "extern01.txt". A prerequisite is that there is at least one SAP GUI window on the desktop (minimized windows are ok).