The lifter being higher up its bore with either a longer valve or a thicker shim would not be a concern. It won't rock in the bore.
As long as the low lobe and high lobe are increased by the same amount (ie. the difference in base circle stays the same) then there is no issue. My feeling says that a bit bigger difference would be acceptable, if the base circle is almost the same I guess there would be difficulties with the system switching from low to high lobe (then there would not be enough 'time' to push the plunger in the bucket to lock the bucket)..