FS2004 Change airport approach

Hi all, what I'd need is to change the approach path, followed by AI aircrafts landing to an airport nestled in the mountains.
I've searched and read something here in the forum, but I really don't understand how to do it. Consider that I don't know what is or what it means for FS, an ILS Approach or FAF or Star Approach.
The situation is as follows:
AI aircraft: the newly released JYAI_AW139 and may be other helicopters or slow-mover GA aircraft
Airport: Trento Mattarello - LIDT. There is a nice addon available on Avsim.
If possible, I need 2 or 3 "turning" points where the aircraft is istructed to follow a certain route, at a given altitude.

Thanks in advance, Giorgio


Resource contributor

First, you can designate three things in the MAIN SECTION of the ILS approach (not in any of the legs)- the IAF point (i.e. navaid or waypoint) , the altitude of the aircraft at that point, and the heading the aircraft will take from that IAF (the planes will approach the IAF from all degrees of the compass). Then the next "point" is the point at which the plane intersects the extended centerline of the landing runway - it will turn and follow the runway course to the runway. The plane will be descending from the IAF to the runway.
Hi Tom, thanks for answering.
In these days I give it a try, taking inspiration from a couple of modified approaches, released time ago in MAIW packages. I've learned and understand something new, but the learning curve is still long.
I added an ILS Approach for RWY18 at LIDT. Aircraft coming from south, lands correctly, not those coming from South-East.
I don't know if this could depend by the airport from which the AC is coming from. Both airports are inside the visual zone of the target airport. LIPX is 39 NM South; LIDA is 18 NM South-East
I have to proceed with other test to fully understand how it works.
Hope to have enough time in the next days.

Thanks again, Giorgio