I wanted to know
1. What makes a program like PL/SQL complex?
2. What kinds of changes to such PL/SQL programs can be said as Complex Changes?
There are two aspects to complexity (to simplify things):
1. Code complexity
2. Business Logic complexity
What kind of change can be said as complex?
At one end of the scale, changing a form colour could be said to be simple. At the other end, deciding to split the contents of a form across several new forms, each with a mixture of both old and new functionality, where new data columns are being used etc could be said to be very complex.
However, that may just be code complexity if the business logic behind it is simple.
A single form with a single button could be said to be simple, but if that button sets off a complex query and generates subsequent reports using relational data from many tables - complex.
So, look at the code complexity (nested loops etc) and look at business logic complexity (an example used before - handling of new orders from a debtor).