Yeah, borrowed neutrals are a major problem here ????
Anyway, where was your N-E bond before the incomer was replaced? If it was in the correct location (before the incoming breaker) you should be just fine to leave in place and your sparks is mistaken.
Your LEDs glowing when "off" is a bit worrying, can you verify that your incoming polarity is correct? Also check the voltage between neutral and earth of your now TT system.
Maybe post a photo of your board with the lid off, a picture is worth many words.