I don't want to have to repaint an entire wall because of one or two
hairline cracks.

I believe I am right in saying that the Dulux paint matching service
only matches to the closest Dulux colour.

How hard is it to tint a colour to get an exact match? Or a match as
near as dammit so that only close inspection would reveal a
difference.

The colour is currently building industry standard magnolia, matt
emulsion.

MM