Pretty straightforward, as the title says in order to turn a RHIB signal into a supply drop you first deploy the RHIB.
Once deployed bring up /skin. In the nearby tab you should see metal double doors, skin these to any other skin and close the /skin window.
Next hit the RHIB with a salvage hammer to turn it back into a signal. The signal will display as the skinned metal double doors in your inventory.
Equip these metal double doors and throw the signal. What arrives will be a supply drop and not a new RHIB.
Voila!
