I suppose I don't 'restore' to "Concourse" condition. I DO use parts & components that are period or year correct. I've installed rebuilt starters that are functionally correct, but surely not the original unit.
I have no qualms about doing a color change from original - but - I DO keep my color choice correct for the year/model. (Then I have the door tag changed to reflect the current color & interior.) My current C/S has had a color change, added dual exhaust (with correct valance & quad tips), Power Brakes, wheel well lip moldings, and am going to add Deluxe interior, Hood stripes, and vinyl top. All correct (but not original) for the year & model.
So I guess, technically, I 'modify' my cars. The only limit I place on myself is to stay within the boundaries of how it COULD have been built originally. But that's just me.
Neil