i don't know how your valences are installed. i had to remove the ones in our trailer and all i can say is you become a contortionist! there were l-brackets screwed into the wall that the valences slip over and then you have to screw a screw up into the l-bracket and into the valence to hold it. i could not position the screwdriver to do this! the blind support bar was covering the hole in the l-bracket.
so i came up with a solution that is much easier, at least for me. i went to the hardware store and bought some 2 inch straight joint menders, some machine screws, washers, and nuts. the l-brackets come out perpendicular to the wall. take one of these menders and screw it into the hole in the bracket. position the mender bar at about a 45 degree angle. what you are doing is positioning the screw hole on the mender out about another inch or so from the wall. this let me slide the valence up onto the l-bracket / mender and then i could screw the mounting screw up through the hole in the mender and into the valance without the blind being in the way. the bracket carries the weight. all the screw is doing is keeping it from shifting.
2015 cardinal model 3825fl
2015 dodge ram 3500 dually