What are the risks in disable MySQL old passwords?

I am in the following scenario:

• I have to develop a new project in PHP 5.4
• The company has several other [important] systems running on PHP 5.2, VB6 and VB.net, using the mysql old password format (16-byte passwords) to connect
• With PHP 5.4, I can't connect to MySQL because the old password error, unless I set the password to the new format (41-byte passwords) with:

SET SESSION old_passwords = 0;

and

SET PASSWORD = PASSWORD('my_old_password')

If I make these changes in mysql (setting passwords to the new format), will the systems in PHP 5.2 and VB continue to connect without problems?

(This question is so old and unpopular, but I really need to answer it for the sake of completeness)

After reading many (really, many) articles on the Internet, there are no documented info about old systems using PHP 5.2 being able to connect with the new password format.

But, if I remember well, my final solution was to upgrade the PHP version running in those important systems.