Replacing a 5V female barrel connector on USB hub with female USB micro
Use of micro-USB receptacle for powering a 4-port USB hub is a poor idea. The official contact rating for micro-USB matching pair is 1.8A only, which is technically insufficient to power all four ports to full capacity.

Regarding the specific questions:

(a)  replacing the power jack barrel with u-USB is possible, but is not easy, unless you will glue the u-USB or secure it somehow else, and use fly wires, since PCB footprints are totally incompatible;

(b) the under 200Ω connection between D+/D- is one of the charging port identification signatures, on the port which supplies power, which will be on the other end of your cable. On receiving end nothing should should be connected to D+/D-.