There is another scenario that is messing the guided rule code after saving, closing and re-opening it using business central.

Steps to reproduce:

1. Create a guided rule.
2. Add a FreeForm DRL field for the LHS (When)
3. Add the following code:

$td : MyTestDateObject( testDate != null )
MyTestDateObject(firstName != null && firstName != "" && eval($td.getFirstName().toUpperCase().equals("NONAME") || $td.getFirstName().toUpperCase().equals("NAMENOTPROVIDED")))

4. Save it
5. Check the source code and you will see that || operator still remains the same.
6. Close and re-open
7. Look again at the source code and the || operator was changed to &&