There is a rigid vang now, but when I sheet in the main the boom hits the top of the dodger.
Something isn't right, then. Either you're not hauling the main up all the way, it's blown-out or the dodger is too high.
Can the rigid vang be adjusted to prevent that from happening?
I don't know, for sure, but, if it could, it would have the same effect as using a topping lift to accomplish the same end: A floppy, misshapen, poorly-performing main. Except perhaps...
Don't quote me on this, but I believe
there are conditions under which a topping lift is used to adjust the shape of the mainsail, in conjunction with vang sheeting. (This would be a performance racing technique.) I don't know if the same can be done with a rigid vang.