Yes its safe to run an Axleback muffler without tuning.
Just for the sake of knowing you can also run a catback exhaust or a midpipe without tuning. The major point of restriction on the 2016 platform is the Jpipe ( Down Pipe on previous years ) Because the axleback has not impact on the air restriction you can replace it without a tune.
Which axle back are you considering? I would love to hear some sound clips before and after if you think about it when you make the swap.
Slow is Smooth > Smooth is Fast