Can a Shabbbos lamp be moved in order to better direct the light or one may only slide the cover over the light bulb?
If the light bulb used is a LED source or fluorescent, it seems that it is permitted to move the Shabbos lamp to better direct the light.
Although a candle is muktzeh, this applies to source of fire (and will apply to an incandescent light bulb) and not to a non-fire source of light. Although some authorities have forbidden moving other light sources, because people will confuse this with fire sources.
Today, when incandescent light bulbs are very much the minority, it does not appear that there is need for stringency in this matter.
See Shemiras Shabbos Kehilchasa 13:14