Koyt, Foyt.............LOL
But yes you can change manufacturers anytime you want to. Used to teams ran different cars at different tracks all the time. Depending on what worked best at short, speedway, and super speedway tracks.
And it would have no effect whatsoever on manufacturers points. Whatever brand runs the race gets the points, it matters not one bit what team fields the car or who drives it.
And if you remeber last season there was a lot of talk that Gibbs would run some Chevy's before season's end with no prohibition.