Short answer - follow the GS down to the new OCA or DA, whichever higher.
The DA cannot be lower than the OCA or the system (ILS/VOR/etc) minima. If the OCA goes up by 50ft, so must the DA. The margins are still there, albeit 'underneath' the extra 50ft you just added on for the new crane/tree/whatever.
You do also need to adjust your visibility minima under EU-OPS, you need to refer to the tables for calculating aerodrome minima in your Ops Manual/Aerad/Jepp Text manual.