The change in absorption from canvas paint is going to be frequency dependent. Higher frequencies may be reflected where they were previously absorbed. However, painted canvas is not near as stiff as drywall, plaster or paneling. To the extent that soundwaves strike the surface and pass through or physically vibrate the canvas there will be some deadening action at lower frequencies, though it may not be the same amount as before.
In short any change is likely to be a fairly complex model that will not be given to yes/no answers. You might try temporarily hanging some painted canvas in the various areas you were thinking of painting and just listen. Who knows, you might prefer the results.
In short any change is likely to be a fairly complex model that will not be given to yes/no answers. You might try temporarily hanging some painted canvas in the various areas you were thinking of painting and just listen. Who knows, you might prefer the results.