Can a Sucah be lowered? Is that like building a Sucah under a tree branch and then cutting the tree branch down after the Sucah is built?
If a Sucah covering is built 30 Amah's high that blocks more sun than it lets in, and then it is "lowered" by building an additional lattice 9 Amah's high that minimally fulfills Lavud (there are no spaces over 3 Tefach but by itself it does not block more sun than it lets in) (but both combined block more sun than it lets in because the first one did by itself), is it a valid Sucah?
Is it possible that R. Yehudah's position is that the height of 40 Amah's (of the Ulam) is OK only because it leads into the 20 Amah's high entrance (of the Hechal)? Thus, as long as a Mavoi is used to ultimately go into an entrance no higher than 20 Amah's, the Korah of a closed Mavoi can be 40 (or more) Amah's high. Similarly the Sucah question above.
If this is possible, would R. Yehuda require lowering the Korah if none of the subsequent entrances inside was 20 Amah's or lower?
Much appreciation for everything,
1) A Sukah built underneath a tree can be make valid by cutting down the branches of the tree that hang over the Sukah and then by placing the Sechach on the Sukah (SHULCHAN ARUCH OC 626:2). In general, as long as the Sechach is moved, it is not considered "Ta'aseh v'Lo Min he'Asuy."
A Sukah that was built higher than 20 Amos can also be made valid by raising the floor of the Sukah and decreasing the distance from the floor to the Sechach to within 20 Amos (and there is no need to shake the Sechach), as is described in the SHULCHAN ARUCH (OC 633:4) and MISHNAH BERURAH (633:12), since the law of "Ta'aseh v'Lo Min he'Asuy" does not apply to kosher Sechach.
2) Rebbi Yehudah's opinion that an entranceway can be up to 40 Amos high (according to Rav) does not appear to have anything to do with additional entrances, or even the height of the Mavoy into which it may lead, as you suggested. The Mishnah and Gemara do not seem to make such stipulations. If so, Rebbi Yehudah would not require lowering the Korah as long as it is within 40 Amos high, regardless of the height of the Mavoy after it.