Brompton owners

Could I get away with sticking a very mild riser bar on an S model without needing to recable brakes and gear?

The cable housing were cut at a very specific length so it fold perfectly, so you might need to get the M type cableset and carefully trim it a bit.

As for the handlebar, you need to find a riser that is 22.2 all the way right until the clamp area, as oppose to 22.2 until the end of the grip part, otherwise it's nigh on impossible fitting them on an Brompton stem.