1) Likely I would analyze as singly symmetric for modifications to only 1 flange. Not sure what structure you're modifying, but maybe that could change the approach. You could analyze both ways for a fun comparison. In general, I can't imagine you're drilling enough under your temporary loads in...
The shorter the column, the higher the shear. Imagine infinitely short columns, and your shear is going to approach some form of PL/AE (A, E, and L for the beam). Stiffness attracts load is another way to think of this problem. Also, think of the curvature (induces bending and shear in this...
Solve for the displacement, then use that to determine the fixed end moments. THEN use the FEM along with moment distribution method. You could probably use some other analysis technique too. There is extra moment carryover to the fixed bases if I remember right.
