I've been messing about with the Finnish Mig-29 and after a lot of trial and error have successfully changed the loadout to 4x RBK500 and 2x R73. Everything seems fine with the R73 but the RBK500 have no animation for when they leave the aircraft and before they hit the ground. They disappear off the hardpoints on the wings as normal but then vanish rather than flying through the air to hit the ground. The explosion on the ground appears correct and makes cluster impact craters.
Have I missed something? Do I need to tweak an option to show the correct dropping effects for the RBK500?
You are missing a TCompositeHappening. Open the ApparenceModel module and look at the Actions list. You should see one TCompositeHappening (for the gun) and two or more TSoundHappening (2 for each missile weapon; I presume for each wing).
You will need to add a TCompositeHappening that contains the correct TBombHappening, so you should find an existing unit that uses the bombs you want, then add the same reference to your custom Mig-29. Make sure your new reference uses a weapon_effet_tag that matches the one in the WeaponManager module. I used the Czech napalm Mig-29 in the example.