I am completely novice in the field of large aircraft composite repairs. However I fly regularly in composite aircraft ( high performance gliders) and there when a (large) repair is done it always adds weight ( unlike in repairs in aluminium or wood/fabric) . For aerodynamically fine tuned gliders , if repair is in fuselage it can affect CG, if it is in or near control surfaces it can add instability and sometime vibrations at certains speed .
Is this irrelevant in large aircraft such as the 787 ?