So for example, If I want to enable all 3 GHA in VHHH (HAS,JASG,SATS) I just add those code to GSX parking customization page and it will be fine?
It should work, but not for Jardine, see below.
btw, JASG=Jardine airport services?
No. Please re-read my previous explanation, where I said to check for the couatl.atc_parking_codes = line. If you did that, you would have notice that Jardine it's just "Jardine", not JASG. That would be the name of the texture, but that's not the parking code. The parking code is the couatl.atc_parking_codes, as I've said in my previous post.
But again, as I've said already in my first reply: ALL of them are ALREADY assigned to VHHH by default, so you shouldn't do anything, and they will just work.
Of course, I tried and, sure enough, I can see them at VHHH.