This issue has been logged for a long time but so far it has just been ignored and the respective ticket deleted/closed due to BIS inactivity. Despite it's relative unimportance it does have a major negative effect on modding and the content making community. Custom textures are a critical part of mission making and reliably being able to change them is key to making professional missions.
Currently SetObjectTexture and its Global counterpart do not work reliably. Custom textures do change but in many cases the results are unreliable at best with either the texture not displaying at all or display is delayed until the viewer is very close to the textured object - i.e. switching in game. This looks very unprofessional and kills the effect the missions maker is trying to achieve.