No law bars the Chief Justice from engaging in business not connected with his position as the highest official of the Supreme Court. Money changing or foreign currency trading is not one of those businesses which he is prohibited from engaging in. Now, it may not be legally wrong, but it is inherently immoral.
As the third highest government official, I am sure that the Chief Justice is privy to information which we, ordinary Pinoys, are not entitled to. And I'm sure that cases involving foreign currency trading malpractices abound in the Court. With this presumption, I am also sure that those involved in these practices are either respondents or accusers.
What bars the Chief Justice from getting such information on currency trading ahead of others? Not one law. This explains why several laws prohibit government officials from engaging in business since every official enjoys extraordinary privileges attendant to their positions.
Likewise, an FX trader, for him to be successful in this trading practice, engages himself with several persons. People bear information critical in deciding to download or upload or exchange currencies to effect interests. What will bar him from seeing or meeting other people which interests are not solely into trading, but in other things, like, say horse-trading cases before the courts?
This explains why several laws discourage government officials from engaging into other businesses while serving government. Due to their positions in the bureaucracy, government officials enjoy the privilege of meeting people of influence, probably even those controlling foreign exchange market in the Philippines. NOthing legally wrong or criminal with meeting people--it is moral destitution that sometimes bar someone from doing so.
Imagine a Chief Justice bank account being used by several people to engage in something which can be "controlled" or effectively managed by people of influence. This opens the issue up to several confusing questions which borders on integrity and honesty and morality, not law.