According the manual it should be possible to change the weapons payload:
Payloads: After selecting a gunship you can change the weapon loadout. You can only change the gunship’s weapons when you are landed at an airbase, carrier or FARP.
To change weapons cycle through the weapons available for each pylon or select a default weapon loadout (air-to-ground, air-to-air or recon/scout).
You may change the weapon loadout for any of the gunships in your flight group. For gunships other than Apache Longbows, Comanches, Havocs and Hokums you can only select the three default options.
I have found all other Buttons which are described in the manual (e.g. Briefing, Log, Save etc.) But where i found the Button to change the Payload? I run 1.16.0 with Javelins Hover Mod.