Yes, not sure how you "feel them out" to be honest. Its kind of pointless if you think about it. 2 scenarios may occur.
1.He is ok with mods. Therefore if you bring it in with mods anyway, he will have been fine with it. No need to find this out before hand.
2.If he is not ok with it. If you ask him or "feel him out" then he will be on the lookout for you having mods on your car. You might as well just bring it in and see what happens.
Not sure feeling out is useful here.