You cannot apply more than one script to a single entity. HOWEVER, you can do better than that.
You could go about this by creating one large script that does everything you want the guard to do.
Or you could combine many different scripts by telling each script at the end to "RUNFPI=[name of next script to run].fpi", where you will obviously replace that bracketed section with the name of the script you want to run. I don't recommend directly changing the default scripts in this manner, as every entity that uses them will be effected, you may want to just copy the default scripts and save them under your own name.
The one and only,
~PlystirE~
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