[sleepycatgirl]

Nope.

It restricts modifications one can do, and how to distribute it.

There is quite a stark difference between source available, and open source.

[praveenperera]

You can modify however you want, you just can't turn around and sell it.

[josephcsible]

No you can't. You're banned from removing their payment nag.

[skeledrew]

Why would you want to remove it? Do you reasonably see yourself digging into the code to remove that bit, rebuilding and reinstalling, compared to tapping "I have paid" once to dismiss (ideally after you actually have paid)?