I think you can follow musicalglass' advice and get a better fit than you've got currently. I find tho, that it's hard to be symmetrical with that approach. I always end up a little shorter/tighter on one side.
Your best best is the disassemble, cut, reassemble, as you mentioned.
One of my best purchases was a book called "Fitting Your Figure". It gives really nicely done beginner instructions on measurements and then how to make alterations based on the fitting problem. https://www.amazon.com/dp/156158083X/ref=cm_sw_r_cp_awdb_imm_t1_zWgUFbX2PRPW5