You cannot simply set a player to forfeit his originally nationality after he gained the nationality of Hong Kong. The mechanism of the game and the real life situation are totally different.
In real life, it is true that a player should give up his original nationality in order to have Hong Kong passport. But in real life, a player can also simply give up his Hong Kong passport and simply get back his own country passport once he is retired.
The Hong Kong passport is only a tool for a player to represent Hong Kong to play in national side and also to play in a league in Asia where he can be treated as an Asian foreigner and easier for him to play there. It is common that player will give up his “new passport” and get back his original motherland passport once he is retired.
But inside the game, if you simply delete his original nationality and only set Hong Kong as his nationality, how could a player get back his own country nationality once he is retired? The game won't support such function to retrieve his original passport.