Yes it went as well as it could. The frame is still alive (~10K miles later) and the hole drilled in the chainstay end cap didn't lead to any issues with cracks etc.
I did however have issue with the custom soldering job inside the bottom bracket that replaced the external junction box. Lots of crap (water/dirt) makes it into there and it eventually corroded things a bit leading to a short circuit and a bike with no gears one day.
I bought a new wiring harness and left the junction box alone and fixed under the BB as intented, then just hacked the battery wire and led that into the bb and seat-tube for an internal battery. So now, the wire from the junction box to the rear mech runs on the underneath of the chainstay and hence the hole drilled is no longer used and covered up to stop fish getting in and swimming around in there