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 decorative material needs sound ordinary support and appropriate fixings. Hidden services and uncertain substrate must be considered before attachment. This task excludes structural reinforcement and should not be used to stabilise an unsound frame through decorative trim.
The visible reveal between trim and frame needs an agreed consistent position. Existing irregularities can affect the result. Replacing decorative material does not authorise reshaping the structural opening or hiding a frame condition that needs separate repair.
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.