Soldering XLR Cables together
For the things one usually uses XLR for (Low impedance audio balanced lines, sometimes RS485 (DMX) and sometimes small DC power, it will likely be absolutely no issue, all this stuff is fairly robust, and it is not like anyone ever claimed that an XLR was a controlled impedance connector (Or suitable for any frequency where one would care). 

On a theoretical level you have an impedance discontinuity and a break in the shield, but I can usually find something actually important to worry about. 

Unless you are doing something weird, it will be fine, but for neatness I would normally fit a male/female connector pair and then just plug them together, in a mad scramble however, tape and twisting will generally work in a pinch.