SE slip-ons are a good choice. Why not do an intake/remap (complete your stage 1 upgrade) and get the most out of your bike right away? The difference over stock is well worth the $$. good luck.
Dennis, welcome to the forum. As glider said, with just a muffler change there is no need to remap and there will be no harm to your bike. If you were to also change to a high flow air cleaner, then you would need to do some sort of remapping.
No remap on my 07 FXDB when CycleShack exhaust system was installed. The Dealer reloaded the ECM for a torque smoothing problem that should have been done anyway on there dime
I've got the SE slip-ons, SE Air Cleaner, and Stage One download on my Electra Glide Classic and am very pleased with it. I like the way it runs, sounds, and I like the 45 MPG I'm getting.