The last bit of the URL is 203 in mine, not mr0. I don't remember what the stock setting was. I think mine got changed to 203 on one of the system updates.
Any system update has the potential to brick your phone. Having said that, the chance of Nokia releasing a Maemo system update is exactly zero. The last such update was in 2010. If your system is older than that then it is very advisable to update it - just once - anyway.