It is file by file. But could be made recursive with a simple loop.

LOCAL lnFiles, laFiles
SET DEFAULT TO 'c:\your directory'
lnFiles=ADIR(laFiles,'*.dbc') &&or *.* etc....
FOR N=1 TO lnFiles
	THISFORM.fileprop.setfileattribute('c:\your directory\'+laFiles[n],'HSRA')
ENDFOR
SET DEFAULT TO

i didnt test that code, but something like that should work.