Yes it does - by connecting all of the live wires you will cause the wall switch not to work and your bathroom light will be constantly on. If you disconnect one of the lives then the loop won't continue to the other lights - or you wont be able to turn the bathroom light on at all. As you are finding - identifying which live wire is which is an absolute nightmare...and its why a 'proper' sparky will mark the switch wires with tiny pieces of insulating tape, or in fact use cable with 'twin reds' that is, indicating that both will be live when the switch is on. The proper way to fit a different light fitting is to move the loop in rose into the loft, and just suppy the new fitting with a neutral, live and earth from there. Sorry I can't be clearer, but if you check out the DIYnot forum, you'll find diagrams in the electrics UK section. Best wishes!
John, April 2009