Top corners and returns need appropriate ordinary cutting and fitting. Show any unusual junctions before ordering material. A compatible profile and adequate lengths matter; filling large mismatches is not equivalent to a properly planned replacement surround.
Agree filling, joint preparation and the painting boundary. A primed replacement can still need final decoration after fitting. Window glazing, specialist seals and rated-door certification are outside the task even where the new architrave sits beside those systems.
The base of an architrave often meets skirting of a particular thickness and shape. Include that junction in the enquiry. Replacing one trim element may expose a mismatch, but changing the entire room’s skirting is a separate decision and scope.
Replace the accepted ordinary decorative surround with suitable joints and fixings, leaving the agreed preparation for finishing. Scope limits: Ordinary decorative surrounds only. No structural jamb or opening modifications, specialist glazing, fire-door certification or hazardous-material disturbance.