Of course they had no choice given the state's 51% stake in the company. Having said that, this was probably a prudent move for a few reasons:
1. Being cooperative now will give them a negotiating edge with the governor in the future.
2. Good PR move: it will publicly demonstrate solidarity with the "povo".
3. Even though billing rates will remain the same, they will continue to grow profits through greater efficiency in their operations and cheaper purchase of energy for resale.
If you look at their last Q report, you will see that many of their purchased energy for sale contracts were signed between 2006-2008 when rates were much higher than they are now. Their three biggest contracts are set to expire between 2013-2015. Since Dilma and co. have forced all provider to drastically cut rates late last year, Copel will have the opportunity to renegotiate their purchase contracts under more favorable terms. At the same time, since the company's own generation capacity has been increased since 2012, more of the energy they are selling going forward will have many of the costs already built in.