The rear sight is not welded on (if it were, how could it be adjustable?). The sight base is welded to the receiver. The sight assembly screws into the base. Look at your rear sight top-down. There is a big honkin screw. Loosen it, and you can adjust the rear for windage. Remove it, and you can remove the entire assembly.
Now slide on, and install the RMR adapter .. and you have an RMR as your rear sight. Not difficult to install. Not difficult to shoot with.
I personally prefer a T1 on an ultra-low mount, which co-witnesses with the SP5k sights. But there is something to be said about the extra bulk/weight of the system in comparison to the RMR.