It seems you can copy the tv_grab_url file, with exact same owner+group and that does the trick.
On my Synology NAS hosting TVHE :
sudo cp tv_grab_url tv_grab_url2
chown sc-tvheadend:synocommunity tv_grab_url2
vi tv_grab_url2 (this is to change its name to "XMLTV: XMLTV URL grabber2")
Restart TVHE and it's there - see screenshot.